The two particular elements are that we have to consider both what mirrors do and what happens when we look into them (lines 48-52).
The explanations may be subject to debate; however, recall that this is a main point question. The main point of the question is not to show that the debate exists; otherwise, the passage would have focused more on points of contention between the two, or reasons to believe one or the other. Instead, the two explanations are simply presented. Hope this helps.
