The background of ______, a novel by Dickens, is set in the French Revolution.

A．only a limited number of chimpanzees are used for sampling the virus.
B．it is now extremely difficult to find chimpanzees that carry the virus.
C．the samples collected are from two different subspecies of chimpanzees.
D．it does not provide reliable evidence of the link between SIV and HIV-1.

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.