In the 20 years since the first cases of AIDS were detected, scientists say they have learned more about this viral disease than any other.
Yet Peter Piot, who directs the United Nations AIDS program, and Stefano Vella of Rome, president of the International AIDS Society, and other experts say reviewing unanswered questions could prove useful as a measure of progress for AIDS and other diseases.
Among the important broader scientific questions that remain:
41. ____
A long-standing belief is that cancer cells constantly develop and are held in check by a healthy immune system. But AIDS has challenged that belief. People with AIDS are much more prone to certain cancers like non-Hodgkins lymphomas and Kaposi’ s sarcoms, but not to breast, colon and lung, the most common cancers in the United States. This pattern suggests that an impaired immune system, at least the type that occurs in AIDS, does not allow common cancers to develop.
42. _
I was ushered to the AIDS ward of a hospice in the slum.I would later learn that the ward did not exist，at least not officially.Not a single person in Thailand had AIDS，according to the Thai government at the time.People got"sick，"of course，sometimes"very sick."but no one had AIDS.The hospice was home to an ever-growing number of"very sick"people.
I entered the ward and was greeted by two Thai nurses.
"Thank goodness you are here，Marc，"said the first.
"You’re a doctor，right"
I shook my head.
"So you are a medical student then!"
I shook my head again.
"But you know medicine，right"
"Kinda，"I offered."I watch E.R.,every Thursday"
After a rapid exchange in Thai，the first one
A. A doctor
B. A medical student
C. A volunteer
D. A government official
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 i
A. potential
B. initiative
C. practical
D. existing
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