It's a better idea to simply post the question than an attachment, because of two reasons:
- some people won't download attachments
- our unregistered visitors won't be able to see the question
So the argument here goes like this:
- self-pollinating primroses seem to be more successful at the production of seeds
- however, they are rare
A does not really help explain the rarity of self-pollinating primroses. The fact that the insects don't discriminate between the two types is no new info, since we're already told in the argument that you can't distinguish between them.
B is correct, because this would help explain the success of non-self-pollinating primroses: their seeds are more robust and likely to produce a mature plant than those of the self-pollinating primroses. This happens even in conditions that are not favorable to non-self-pollinating primroses (lack of insects to carry the pollen) and that should tick the balance in favor of the other type. However, this is not the case.
C doesn't really address the paradox, since we're not comparing two types of self-pollinating plants, we're comparing those that can self pollinate and those that can't.
D might be true, but again does not explain the paradox. It needs to compare the two types!
E is already stated in the argument, so it's no new info. Again, no comparison between self-pollinating and non-self-pollinating.