Just wanted some clarification on my thought process!
I chose E at first because -
Passage A did introduce Solnick and Hemenway to support the argument, but upon closer read, S & H doesn't introduce the main topic, but the main topic is introduced, and then S & H is used to bolster that argument.
Passage B presents S & H's study to introduce a different view on how to explain its results, but doesn't argue against the study itself.
The correct answer choice D -
Passage A uses S & H to provide evidence for rivalry
Passage B uses S & H as a rhetorical question to discuss the explanations for the results of the study.