单项选择题

It can be learned from the passage that______.

A．it will be difficult for scientists to develop a vaccine for women
B．HIV infects women in the same way with men
C．most women have contracted a variety of HIV from several men
D．it will be easy to develop a vaccine for men

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单项选择题

The author's attitude towards the developing of HIV vaccine is______.

A．pessimistic
B．optimistic
C．positive
D．objective

单项选择题

It will be even more difficult to develop a vaccine because______.

A．most women are infected by a single variant of the HIV virus
B．the virus can duplicate itself into more genetic variants
C．it is difficult to monitor the activities of the viruses
D．technologies are not advanced now