Based on the customs of countries such as Mexico and an analysis of an

Dear prajaktt,

I'm happy to respond. MGMAT always has good questions. This one is particularly tricky.

First of all, for listing examples on the GMAT, we need to used "such as" (e.g. "countries such as Mexico"). It is entirely incorrect to use "like" (e.g. "countries like Mexico"). We can reject (C), (D), and (E).

This leaves us with the sophisticated split between (A) & (B). What is "based" on what? Literally, the "base" of something is its bottom: for example, a building is "based" on its foundation. GMAT uses this term metaphorically, to indicate the logical basis of of something. Thus, an idea or a conclusion or an inference can be "based" on some evidence.

Also, as a participle, "based" is a noun-modifier, and begins a phrase that goes all the way up to the comma. The noun this phrase touches, right after the comma, is the target noun. In (A), the sentence says that the "historians" themselves are "based on the customs." That's pure nonsense. People cannot be based on ideas.

Instead, the action of the historians, their inferring, is based on something. For this, we need a verb-modifying phrase. Using a prepositional phrase solves this problem, because "on the basis" can be a verb-modifying phrase, modifying the action, "have inferred." Indeed, this inference was "based" on the "customs." The answer has to be (B).

Does all this make sense?
Mike