Lets say if C) was somehting absurd then the next best would be D),correct?

Also in your opinion what would be a convincing reason to not go with D)?

D is just irrelevant, and even if C weren't there, D still wouldn't strengthen the argument. The fact that the monkeys don't eat these millipedes has no bearing on the question of whether their reason for rubbing their bodies with them has to do with repelling mosquitoes. I don't see how one could make a case for D. I'm curious as to why some people want to go for D, though. How does it look as if it would help?

Cant make any strong points for d) so selfdismissed it.

Thanks Karen for your inputs in this forum. It's always to good to have a Vebal expert in the house

Actually I got baffled by 'rarely' in option C and hence didn't choose it but instead went with A. Can someone please explain why A is wrong ???

A single millipede is rubbed by several monkeys - which strengthens the conclusion that the secretions from the millipede are effective in repelling the mosquitoes. In fact so effective that one millipede can be used by several monkeys.

- pradeep

A says that they rub their bodies with the same millipede, but it doesn't suggest why they do it. For example, maybe they do it for some social bonding--we don't know.

C directly addresses that they are more likely to do it when it's raining, and that it could be due to the increase of mosquito population.

C is the best option