单项选择题

The biggest worry that the researchers now have is ______.

A．more and more wild chimpanzees are being slaughtered
B．AIDS virus is difficult to be killed and controlled
C．it is not easy to repair people's deficient immune systems
D．many dangerous viruses are being transmitted to humans
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单项选择题
Since chimpanzees are genetically very similar to humans, ______.
A．chimpanzees are likely to suffer AIDS just like humans if they are infected
B．it does not matter if human beings are infected with SIV rather than HIV-1
C．we can use human vaccines to prevent chimpanzees from getting AIDS virus
D．AIDS vaccines based on chimp's immune mechanism are possible to be made
单项选择题
What is exceptionally remarkable about a child is that ______.
A．he is born with the capacity to speak
B．he has a brain more complex than an animal's
C．he can produce his own sentences
D．he owes his speech ability to good nursing
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