Can someone please help explain? The answer is E. I don't see why D cannot be the correct answer. The phrase "partly because" in D parallels the "partly because" in the main clause, whereas the "partly to acquire" in choice E does not parallel exactly. I know the wording "should be acquired by their steers" in D sounds strange, but I don't see how it is wrong: depending on context, maybe the breeders do feel that the characteristics SHOULD be acquired by their steers in order for their economic purposes to be fulfilled..?

In recent years cattle breeders have increasingly used crossbreeding, in part that their steers should acquire certain characteristics and partly because crossbreeding is said to provide hybrid vigor.

A) in part that their steers should acquire certain characteristics
B) in part for the acquisition of certain characteristics in their steers
C) partly because of their steers acquiring certain characteristics
D) partly because certain characteristics should be acquired by their steers
E) partly to acquire certain characteristics in their steers