I selected answer choice A (D is correct) for this one. To be honest, I see both A and D mentioned in the lines preceding line 57 where the term "succession" is cited from. I've read my share of dense material but I honestly cannot discern what information the author is trying to tell me in the sentence starting on line 50 with "Today, the Nicaraguan pines occur...".
How is it clear that the term "succession" is referring to the succession of answer D over answer A when they are both explicitly listed prior to the terms use, in the same paragraph being referenced?
Goddamn trees.