I mapped out the stimulus

X → A

Y → B

B→/A

When I was reading the answer choices, I immediately interpreted the subject as (X or Y) and (A or B). If there wasn't enough subjects or conditional chains then I marked it as wrong.

a.) Mentally associated animals species with narrow diets with X and will have more difficultly with A. Then I stopped because there was a no new subject.

X → A

Y →/A

b.) The answer choice is the right one because it has the correct number of subjects and conditional chains.

X →A

Y→B

B→/A

Interested!!