题目内容
（请给出正确答案）
Why did Perth develop very slowly at the beginning according to the introduction？
A．It was occupied by Britain.
B．It was a wetland.
C．It scarcely contacted the other cities.
D．It had no rich natural resources.
如果结果不匹配，请 联系老师 获取答案
更多“Why did Perth develop very slo…”相关的问题
Why does the author mention Columbia University in lines 9 and 10？
A．Hazen and Brown developed nystatin there.
B．Brown was educated there.
C．Hazen did research there.
D．It awarded a prize to Hazen and Brown.
Why did the people in Perth turn on their lights？
A．Because it was time for them to wake up.
B．Because they wanted to greet John Glenn.
C．Because they wanted to see Friendship 7.
D．Because they wanted to build the tracking station.
Among the devastating consequences of AIDS has 【21】______ its epidemic spread in the developing world. The disease has caused 【22】______ suffering, debilitation, loss of life and disruption of family, social and economic 【23】______ Because of the considerable expense and logistical difficulty in providing antiviral drugs to populations 【24】______ with the Human Immunodeficiency Virus 【25】______ the world, the biomedical community is looking towards vaccines to help solve this compelling problem.
The search for an AIDS vaccine began more than 15 years ago with great 【26】______ and high expectations. With the 【27】______ of the Human Immunodeficiency Virus (HIV) as the cause of AIDS, it seemed that a 【28】______ would follow closely behind. But despite a large concerted effort, the problem has proven more difficult than 【29】______ , and progress has not 【30】______ the 【31】______ hopes. Here I review the 【32】______ scientific obstacles confronting the development of an effective HIV vaccine, and I consider 【33】______ strategies to overcome these obstacles.
It is instructive to consider the circumstances that have 【34】______ to past successes in vaccine development. The smallpox vaccine is 【35】______ the most successful inventions in the history of 【36】______ Why, 200 years ago, without the benefit of modern biotechnology, did the smallpox vaccine succeed so readily while an AIDS vaccine 【37】______ elusive？ The answer lies in an experiment of nature that provided, to an astute observer, a clear direction for smallpox vaccine development. In this classic story of 【38】______ discovery, Edward Jennet noticed that milk maids who had previously contracted cowpox were 【39】______ to smallpox infection. This observation was the critical event leading to the finding that the cowpox virus cross-reacted immunologically with the smallpox virus and could 【40】______ be used to protect against smallpox.
【21】
A．on
B．with
C．been
D．about
Why did the girls want to be late for school？
A．They did not like school.
B．They had not done their homework.
C．They did not want to take a test.
Why did the man go to school on foot？
[ A] No bus ran in that direction.
[B] The school was near.
[ C] His family was poor.
Why did the man want to exchange the pen？
A．Because of the color.
B．Because it is too expensive.
C．Because it is too cheap.
D．Because it doesn’t work.
Why did they want to try that one？
A．Because it is about family life.
B．Because they know nothing about it.
C．Because there is violence in it.
D．Love story.
