Carcass wrote:
C and D are both good answers. However, only D is the right one.
Actually, we care about of the discrepancy in population density. If we are in a scenario in which the population itself is not being tested for some reason from an inside point of view (they are aggressive) so we do have the answer.
C, on the other hand, shows a reasoning from the outside: the habitat is not accessible and we didn't test the gorillas. However, we do not know if tomorrow (maybe a massive deforestation) we could test them
D instead: deforestation or not even though they are accessible would not be tested either way because aggressive.
Hope this helps.
Regards
Actually there has been no hint either in the passage or question intrinsic factors should be considered over extrinsic moreover even if you consider deforestation
That is future event and should we consider it ?