单选题
HIV Vaccine Reduces Infection

The vaccine -a combination of two earlier experimental vaccines -was given to 16,000 people in Thailand. Researchers found that it reduced by nearly a third the risk of contracting HIV, the virus that lcads to Aids.
It has been hailed as a significant, scientific: breakthrough, but a global vaccine is still some way off. The study was carried out by the US army and the Thai government over seven years on volunteers - all HIV - negative men and women aged between 18 and 30 - in parts of Thailand.
Half of the volunteers were given the vaccine, while the other half were given a placebo - and all were given counselling on HIV/Aids prevention. Participants were tested for HIV infection every six months for three years. The results found that the chances of catching HIV were 31.2% less for those who had taken the vaccine - with 74 people who did not get the vaccine infected and 51 of the vaccinated group infected.
The vaccine is based on B and E strains of HIV that most commonly circulate in Thailand not the C strain which predominates in Africa. "This result is tantalisingly encouraging. The numbers are small and the difference may have been due to chance, but this finding is the first positive news in the Aids vaccine field for a decade," said Dr Richard Horton, editor of the Lancet medical joumal.
"We should be cautious, but hopeful. The discovery needs urgent replication and investigation. "
Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases said: "For the first time, an investigational HIV vaccine has demonstrated some ability to prevent HIV infection amorig vaccinated individuals. "
"Additional research is needed to better understand how this vaccine regimen reduced the risk of HIV infection, but this is certainly an encouraging advance for the HIV vaccine field. "
The findings were hailed by the World Health Organization (WHO)and the Joint United Nations Programme on HIV/Aids (UN/Aids). They said while the results were" characterised as modestly protective... [they] have instilled new hope in the HIV vaccine research field".

单选题 What findings did WHO and UN/Aids reach according to this article?
【正确答案】 A
【答案解析】第一段第二句：Researchers found that it reduced by nearly a third the risk of contracting HIV, the virus that leads to Aids(研究者发现它可以降低近三分之一感染HIV，艾滋病病毒的风险)。这里的“it”指的是上文中提到的新的疫苗”vaccine”。而从第六段我们可以得知科学家们还需要另作实验来研究疫苗是怎么起到作用的，所以B选项错误。选项中只有A才是WHO的最新发现。
单选题 What is the new vaccine composed of?
【正确答案】 A
【答案解析】文章第一段的第一句对该新疫苗的组成就做了说明：The vaccine-a combination of two earlier experimental vaccines(新的疫苗是早期两种实验疫苗的组合)。所以此题正确答案为A。
单选题 What happened to the participants given a placebo?
【正确答案】 B
【答案解析】由题干关键词”placebo”定位到第三段，该段就实验详情做了说明，最后一句：with 74 people who did not get the vaccine infected and 51 of the vaccinated group infected(注射疫苗的一组中51人感染了艾滋病病毒，而未注射该疫苗的一组中有74人感染)。由此可见正确答案为B。
单选题 What is the new vaccine based on?
【正确答案】 D
【答案解析】由题干关键词”based on”定位到第四段第一句：The vaccine is based on B and E strains of HIV that most commonly circulate in Thailand not the C strain which predominates in Africa(这种疫苗是基于泰国最常见的B和E艾滋病毒菌株，而不是常见于非洲的C菌株)。可见，该题正确答案是D。
单选题 What is the significance of this finding?
【正确答案】 C
【答案解析】该题问的是此项发现的重大意义。文章结束语：They said while the results were "characterised as modestly protective…[they] have instilled new hope in the HIV vaccine research field"(他们(世界卫生组织和联合国艾滋病计划署)表示虽然结果被形容为温和的保护，但是该发现给艾滋病疫苗研究领域带来了新的希望)。所以正确答案为C。