SAT Question 261f4ca6: Boundaries answer and explanation

Choice A is the best answer. The convention being tested is punctuation use between a verb and its object. No punctuation is needed between the verb “created” and its object “floating farms called ‘chinampas.’” The object helps complete the idea of the verb—in this case, it explains what the Aztec people created—and any punctuation between the two results in an ungrammatical sentence.