It Is Believed That HIV Has Passed from Chimps to Humans

Multiple Choice

It is believed that HIV has passed from chimps to humans more than once. This suggests that animal-to-human viral transmissions may be more common than previously thought. What is the best evidence in support of the conclusion that HIV made the chimp-to-human leap more than once?

A) HIV has multiple strains, and the virus does not appear to be able to leap from humans back to chimps.
B) HIV has appeared on multiple continents.
C) Human-to-human transmission of HIV requires direct personal contact that simply could not have resulted in the widespread outbreak we see today.
D) Several species are known to have similar viruses resulting in immunodeficiency diseases.