首页 > 外语类考试> 大学英语四级

题目内容（请给出正确答案）

[主观题]

Atmospheric pressure can support a column of water up to 10 meters high. But plants can mo

ve water much higher. the sequoia tree can pump water to its very top, more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stem of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest tress, have unusually low root pressures.

If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask.. How does it get there？ According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results form. the evaporation of water at the top of the plant. As water is lost form. the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion(the attraction between water molecules)are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken.

How many theories does the author mention？

A．One

B．Two

C．Three

D．Four

查看答案

如果结果不匹配，请联系老师获取答案

您可能会需要：

重置密码查看订单联系客服

安装优题宝APP，拍照搜题省时又省心！

更多“Atmospheric pressure can suppo…”相关的问题

第1题

The passage answers which of the following questions？A．What is the effect of atmospheric p

The passage answers which of the following questions？

A．What is the effect of atmospheric pressure on foliage？

B．When do dead cells harm plant growth？

C．How does water get to the tops growth？

D．Why is root pressure weak？

点击查看答案

第2题

The difference between mountain climbing and shipwreck diving lies in ______.A．the amount

The difference between mountain climbing and shipwreck diving lies in ______.

A．the amount of oxygen

B．the atmospheric pressure

C．the breathing rate

D．the damaging degree of the human nervous system

点击查看答案

第3题

The word this in Paragraph 3 refers to______.A．the effect of the hot and cold aspects by t

The word this in Paragraph 3 refers to______.

A．the effect of the hot and cold aspects by the sun on the earth

B．the distribution of the earth's atmospheric pressure

C．the solar-weather interactions

D．the warming effect of carbon dioxide

点击查看答案

第4题

High Dive kilometers up into the atmosphere.（1). No one has ever leapt from such a height

High Dive

kilometers up into the atmosphere.(1). No one has ever leapt from such a height or gone supersonic without an airplane or a spacecraft. Yet Stems, an airline pilot, is not the only person who wants to be the first to accomplish those feats. Two other. have people an Australian man and a Frenchman, are also planning to make similar leaps.

(1). First, she'll climb into a cabin hanging from a balloon the size of a football field. Then the balloon will take her high into the's trato sphere -- the layer of Earth's atmosphere 12 to 50 kilometers above the planet. "The ascent will take two and a half to three hours." said Stems.”Tll be wearing a pressurized, temperature-controlled space suit.”

At 40 kilometers, Stems will be able to see the gentle curve of Earth and the blackness of space over head. Then she'll unclip herself from the cabin and dive headfirst, like a bullet, into the atmosphere.(3) For high dive, astronaut escape suits are a key to success. Current pilot and astronaut escape suits are guaranteed only a maximum altitude of 21 kilometers. Del Rosso, a NASA engineer of spacesuits and life — support systems, said the suit designed for Stem's jump could serve as a model for the lethal environment of higher climbs.(4)

The first hazard is oxygen-deficient air. Any person without an additional oxygen supply at 40 kilometers would die within three to five seconds. The second hazard is low atmospheric pressure. Atmospheric pressure is much lower at high altitudes than it is at sea level. The low atmospheric pressure of the upper stratosphere causes the gases in body fluids to fizz out of solution like soda bubbles.(5)Other hazards include temperatures as low as 55 degrees Celsius, flying debris, and solar radiation.

For Stems to survive, her spacesuit will have to protect her from all of these hazards. "A spacesuit is like a one-person spaceship," Del Rosso explained. "You have to take everything you need in a package that's light enough, mobile enough, and tough enough to do the job. You can't exist without it."

feat n. 技艺的表演

stratosphere n. 同温层

pressurize v. 加压，增压

lethal adj. 致死的

fizz v. 嘶嘶响

debris n. 碎片

A. It will handle several major hazards.

B. Escape suits are tough enough to stand the atmospheric pressure of the upper stratosphere.

C. From there, she'll take a death-defying leap back to Earth at supersonic speed.

D. "In 30 seconds, I'll be going Mach speed," said Stems.

E. How will Stems make her giant jump？

F. In short, blood boils.

点击查看答案

第5题

High Dive Cheryl Sterns aims to go boldly where no human has ever gone before in a balloon

High Dive

Cheryl Sterns aims to go boldly where no human has ever gone before in a balloon: 40 kilometers up into the atmosphere. (46) No one has ever leapt from such a height or gone supersonicl without an airplane or a spacecraft. Yet Sterns, an airline pilot, is not the only person who wants to be the first to accomplish those feats. Two other brave people, an Australian man and a Frenchman, are also planning to make similar leaps.

(47) First, she’ll climb into a cabin hanging from a balloon the size of a football field2. Then balloon will take her high into the stratosphere—the layer of Earth’s atmosphere 12 to 50 kilometers above the planet. “The ascent will take two and a half to three hours,” said Sterns. “I’ll be wearing a fully pressurized, temperature-controlled space suit.”

At 40 kilometers, Sterns will be able to see the gentle curve of Earth and the blackness of space over head. Then she’ll unclip herself from the cabin and dive headfirst, like a bullet, into the atmosphere. (48)

For high dive, astronaut escape suits are a key to success. Current pilot and astronaut escape suite are guaranteed only a maximum altitude of 21 kilometers. Del Rosso, a NASA engineer of spacesuits and life-support systems, said the suit designed for Stern’s jump could serve as a model for the lethal environment of higher climbs. (49) The first hazard is oxygen-deficient air. Any person without an additional oxygen supply at 40 kilometers would die within three to five seconds. The second hazard is low atmospheric pressure. Atmospheric pressure is much lower at high altitudes than it is at sea level. The low atmospheric pressure of the upper stratosphere causes the gases in body fluids to fizz out of solution like soda bubbles. (50) Other hazards include temperatures as low as — 55 degrees Celsius, flying debris, and solar radiation.

For Sterns to survive, her spacesuit will have to protect her from all of these hazards. “A spacesuit is like a one-person spaceship,” Del Rosso explained. “You have to take everything you need in a package that’s light enough, mobile enough, and tough enough to do the job. You can’t exist without it.”

A. It will handle several major hazards.

B. Escape suits are tough enough to stand the atmospheric pressure of the upper stratosphere.

C. From there, she’ll take a death-defying leap back to Earth at supersonic speed.

D. “In 30 seconds, I’ll be going Mach (马赫) speed,” said Sterns.

E. How will Sterns make her giant jump？

F. In short, blood boils.

(46)

点击查看答案

第6题

Ear Discomfort When Flying By Robert James It is quite widespread to respond passengers

complaints of ear discomfort when flying or right away after takeoff. Most complaints arise in the time of takeoff or landing. The air pressure inside the passenger cabin may cause your ears to pop. This could lead, at landing or takeoff, to temporary hearing loss or simply ear discomfort. These side effects usually last only while you are flying and, after a short time, should get back to what is normal for you. They result from a difference between air pressure in the part of your ear called the "middle ear" and the atmospheric pressure of the plane. You can do a number of things to reduce the effects of flying on hearing. Yawn, chew gum, or suck on a hard candy. Keep swallowing, using a glass of water or another drink, but not alcohol. Do this regularly, every 15 to 30 seconds as necessary. Some people have reported that earplugs also help but, so far, there has been no medical study to prove that earplugs really help. You are going to benefit from postponing your flight in the event you are suffering from either infected ears or sinuses, allergies or from the feeling of a stuffed up head. If you have to travel, ask your family doctor or local pharmacist for advice and about decongestants you can use. Many doctors recommend that you use a decongestant spray about 20 minutes before you fly. It is important not to use the spray for more than five days continuously.

What is the subject of the article？

A．The side effects of some medicines.

B．The causes of hearing loss.

C．The function of the ears.

D．The effects of flying on hearing.

点击查看答案

第7题

In May 1989, space shuttle "Atlantis" released in outer space the space probe "Megal-lan",

which is now on her 15-month and one-billion-kilometer flight to Venus. A new phase in space exploration has begun. The planet Venus is only slightly smaller than the earth; it is the only other object in the solar system, in fact, that even comes close to the earths size. Venus has a similar density, so it is probably made of approximately the same stuff, and it has an atmosphere, complete with clouds. It is also the closest planet to the earth, and thus the most similar in distance from the sun. In short, Venus seems to justify its long-held nickname of "the earths twin". The surface temperature of Venus reaches some 900 degree F. Added to that is an atmospheric pressure about 90 times the earths. High overhead in the carbon dioxide(CO2)that passes for air is a layer of clouds, perhaps 10 to 20 miles thick, whose little drops consist mostly of sulfuric acid(H2SO4). Water is all but nonexistent. Born with so many fundamental similarities to the earth, how did Venus get to be so radically different？ It is not just an academic matter. For all its extremes, Venus is a valuable laboratory for researchers studying the weather and climate of the earth. It has no the earths oceans, so the heat-transport and other mechanisms are greatly simplified. In addition, the planet Venus takes 243 earth-days to turn once on its axis, so incoming heat from the sun is added and distributed at a more leisurely, observable pace. Question: The main idea of this passage is about______.

A．problems of space travel

B．scientific methods in space exploration

C．the importance of Venus to the earth

D．conditions on Venus

点击查看答案

第8题

A Canadian researcher has discovered that sound travels 【21】______ air more than one-haft

kilometer an hour slower than had been believed. The discovery has surprised many engineers and scientists who learned they had been 【22】______ the wrong speed of sound for many years.

The speed of sound in air had been 【23】______ to be three-hundred-thirty-one-point-two-nine meters a second. But Doctor George Wong found, 【24】______ accident, that the speed of sound is only three-hundred-thirty-one-point-one-three meters a second. That is a difference of about sixteen centimeters a second.

Doctor Wong is a member of the National Research Council of Canada. He was studying ways to 【25】______ exactly the sound created by microphones. One of his experiments 【26】______ a number he could use to find the speed of sound. He was 【27】______ to learn that the speed of sound was slower than scientists had thought.

To explain the difference, Doctor Wong spent eighteen months 【28】______ past test research on the speed of sound. He finally found the 【29】______ of the difference. It was a mathematics mistake 【30】______ in Nineteen-Forty-Two by physicist H-C Hardy.

Doctor Wong's 【31】______ does not mean a big change for the science of sound. This is 【32】______ Doctor Hardy and Doctor Wong measured the speed of sound for what is called " standard air".

Standard air exists only 【33】______ thought. It is a way for scientists to agree 【34】______ the same speed of sound. 【35】______ the air around us, standard air always has a temperature of zero degrees Celsius and the same atmospheric pressure 【36】______ the air at sea level. Standard air al ways have same amounts of nitrogen, oxygen, carbon dioxide and 【37】______ gases. And in standard air, the speed of sound does not change.

The change in the new speed of sound is 【38】______ small to affect the work of most sound scientists and engineers. But scientists say Doctor Wong's discovery may 【39】______ improve instruments 【40】______ use the speed of sound to measure very short distances.

【21】

A．through

B．on

C．to

D．pass

点击查看答案

第9题

In the atmosphere, carbon dioxide acts rather like a one-way mirror—the glass in the roof

of a greenhouse which allows the sun's rays to enter but prevents the heat from escaping.

According to a weather expert's prediction, the atmosphere will be 3 ℃ warmer in the year 2050 than it is today, if man continues to burn fuels at the present rate. If this warming up took place, the ice caps in the poles would begin to melt, thus raising sea level several meters and severely flooding coastal cities. Also. the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere, possibly resulting in an alteration of earth's chief food-growing zones. In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet. But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of warming, in other words, by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels.

Satellite pictures show that large areas of Antarctic ice are already disappearing. The evidence available suggests that a warming has taken place. This fits the theory that carbon dioxide warms the earth.

However, most of the fuel is burnt in the northern hemisphere, where temperatures seem to be falling. Scientists conclude, therefore, that up to now natural influences on the weather have exceeded those caused by man. The question is: Which natural cause has most effect on the weather？

One possibility is the variable behavior. of the sun. Astronomers at one research station have studied the hot spots and "cold" spots (that is, the relatively less hot spots) on the sun. As the sun rotates, every 27.5 days, it presents hotter or "colder" faces to the earth, and different aspects to different parts of the earth. This seems to have a considerable effect on the distribution of the earth's atmospheric pressure, and consequently on wind circulation. The sun is also variable over a long term: its heat output goes up and down in cycles, the latest trend being downward.

Scientists are-now finding mutual relations between models of solar-weather interactions and the actual climate over many thousands of years, including the last Ice Age. The problem is that the models are predicting that the world should be entering a new Ice Age and it is not. One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia of the earth's climate. If this is tight, the warming effect of carbon dioxide might thus be serving as a useful counter-balance to the sun's diminishing heat.

It can be concluded that a concentration of carbon dioxide in the atmosphere would ______.

A．prevent the sun's rays from reaching the earth's surface

B．mean a warming up in the Arctic

C．account for great changes in the climate in the northern hemisphere

D．raise the temperature of the earth's surface

点击查看答案

长沙黎曼智能科技有限公司版权所有 ©2024

湘ICP备19009690号-1 湘公安备案43019002001016号营业执照

违法和不良信息举报电话：400-118-7898

举报/反馈/投诉邮箱：deng＃ujigu.com（请将＃替换成@）