Hi
AndrewN,
I hope you're doing fine.
This question caught my attention after receiving it my PM. Though, (D) is the correct choice here, and I do refute that, (C) doesn't look half bad.
Many experts, including Charles, have opined on the "ambiguity" surrounding the usage of "those" in (C), citing it can refer to "eggs". But, as per logic, "those" can refer only to "the nests". Pronoum ambiguity is an issue when one can construe multiple meaning through a sentence because of the placement of an "ambiguous" pronoun. But, here I believe, the second meaning is being forced to cause "pronoun ambiguity", for, per logic, no bird can lay eggs of an another bird in nature. So, "those" can refer only to "the nests" here.
(C)
female cowbirds use the nests of other birds to lay up to 40 eggs a year, including the nests of warblers, etc. Here, "including the nests of x,y,z" refers to "the nests of other birds" in the preceding clause, and the "including the nests of x,y,z" phrase adds information about the group of "different nests" that cowbirds use to lay eggs. And this meaning doesn't look bad to me.
What are your thoughts on this?