One of the reasons I eliminated choice E was because ”any” would signal that even the smallest similarity in DNA would indicate interbreeding, but the stimulus says there is a “significant” difference between DNA. To me, this points to there being a small similarity, not a complete difference, which makes the argument fall apart. Is my approach correct?

How can we not interpret “coffeehouses that are well designed” to mean that there are coffeehouses that are well designed; therefore, most of those have art? I thought “that” was a modifier

I believe he means that if the answer choice begins with "presumes/assumes that...", then the remaining language must be descriptively accurate. This is because that answer choice uses reasoning already mentioned/provided in the argument BY the author.