A and D How do I decide between two answer choices when they are very similar?

I was ultimately choosing between A and D and I chose A because I thought that the author in Passage A admitting to the credibility of the objections meant that they weren't completely advocating for it. And the wording used to describe the tone of Passage B was too similar in A and D to choose my answer that way. How should we approach selecting answer choices when we've narrowed it down to two that are very similar?