题目内容
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A．All sharks have teeth.
B．A shark can have six rows of teeth.
C．A shark can have hundreds of teeth.
D．All sharks have extremely sharp teeth.
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更多“A．All sharks have teeth.B．A sh…”相关的问题
A．All sharks have teeth.
B．A shark can have six rows of teeth.
C．A shark can have hundreds of teeth.
D．All sharks have extremely sharp teeth.
A．There were sharks in the sea.
B．She was injured.
C．She didn't have time to swim.
D．The water wasn't warm enough.
Which of the following is a feature that the hammerhead shark shares with other sharks？
A．They have slender bodies.
B．They have wide lobes.
C．They use electroreceptors to detect prey.
D．They sense electric fields from far away.
(47)The great white grows to between 5 and 8 meters long and can weigh more than 1300 kilograms. It can swim through the eater at speeds reaching 32 kilometers per hour. However, one of the fastest swimmers in the shark family is the blue shark, which can swim at a speed of nearly 752 kilometers per hour.
(48)They can grow as long as 5 centimeters, and they are very sharp. Unlike humans, who have two sets of teeth in their life time, some sharks can have as many as 5 or 6 sets. It is rare for a shark to have fewer than 4 sets. It is rare for a shark to have fewer than 4 sets. As the shark's teeth are worn out, they fall out and are replaced by the next row.
(49)In a lifetime some sharks can grow and lose between 10,000 and 30,000 teeth.
Sea biologists have discovered that the shark has a remarkably large brain and a well-developed sensory system. The animal has an extraordinary sense of smell and excellent vision.
(50)Special sensory pits on the shark's nose and chin can detect weak electrical fields in the water that are produced by fish and other animals. Scientists have concluded that sharks associate food with electrical fields. Scientists also believe that sharks create their own electrical fields to aim them in knowing where to go in the sea.
A. Must of the species are not particularly cruel.
B. Sharks have lived on earth for more than 180 million years.
C. The great white is the largest and cruelest of all animals known to attack humans.
D. Some sharks can wear out a full set of teeth in less than 6 months.
E. One of the most unusual aspects of the shark is its teeth.
F. But sharks are also sensitive to electrical fields.
It's a classic mystery of the deep. Why does the hammerhead shark (双髻鲨)have the bizarrely shaped head from which it gets its name？
There have been a variety of suggested explanations. Some simply say that the sharks use their heads to "hammer" and pin down their favourite food. More plausibly, others have speculated that the wide lobes(圆形突出部分)of the hammerhead allow it to have longer electrorecep-tots, the organs that all sharks use to detect the electric fields produced by nearby prey. This might allow hammerheads to sense subtler electric fields from more distant prey than their narrow-headed cousins.
Now it turns out that the shark's head does indeed help it find and capture prey, but not in the way that zoologists expected. Stephen Kajlura and Kim Holland of the University of Hawaii at Manoa set out to test the conventional theory by tricking young sharks into chasing phantom (虚构的)prey. Using a system of wires on the bottom of a shallow pool, they set up electric fields that mimicked those created by the bottom-dwelling shrimp and fish that form. the sharks' usual diet.
Sure enough, hungry sharks abruptly turned towards an electric field when they detected it. But when the researchers measured the distance at which this happened they found it was the same for 13 young hammerheads as it was for 12 young sandbar sharks(沙堤鲨),which have normal-shaped heads.
The two types of sharks proved equally adept at sensing the electric fields: each was able to detect the source from up to 30 centimetres away. That ruled out any improved sensitivity from the wider head. However, the hammerheads enjoy another more prosaic(平淡无奇的)advantage: their wider heads let them sweep more than twice as wide a swathe of the seafloor as they swim, which must boost their chance of encountering food.
The researchers also found that hammerheads could turn more sharply when they detected the phantom prey. "They're a much more bendy shark , "says Kajlura, who is now at the University of California at Irvine. In part, that's because they have more slender bodies than the sandbar sharks. However, Kajiura has other unpublished data that suggests that the hammerheads' broad heads can act as fins to improve manoeuvrability(机动性).
So far, the researchers have only experimented with young sharks, so adult hammerheads may gain some other advantage from their head shape.
The passage is mainly about ______.
A．the different species of sharks
B．the differences between hammerhead and sandbar sharks
C．how hammerhead sharks detect their prey
D．special functions of the hammerhead sharks
What do they get the agreement on？
A．All companies have problems.
B．Small companies have problems.
C．Large companies have problems.
D．There are no problems in companies.
We have two copies left. Keep______ for the file.
A．all
B．each
C．neither
D．either
One implication in this passage is that ______.
A．all RDAs have been established
B．not all RDAs have been established yet
C．it's not important to know RDAs
D．RDAs are necessary only for sick people
Which of the following did the caller have decorated？
A．All the rooms.
B．The living room.
C．The living room and the kitchen.
What is the main idea of the passage？
A．All senses have their limitations.
B．Insects are more sensitive to colour than man.
C．Man has not fully utilized all his senses.
D．Man is not as good as animals in learning about the environment.
