GMAT Critical Reasoning (CR) | Re: The earliest Mayan pottery found at Colha, in Belize, is

I eliminated (D), because I assumed that the stem already offered a premise that "the designs are strikingly different from the designs of the stone implements produced by other cultures known to have inhabited the area in PREHISTORIC times."

IMO, it all boils down to whether 4500 years ago (or approx. 2500 years B.C.) is PREHISTORIC. After thinking a bit about it, I would say NO. So therefore => (D). But I still don't understand why this question is ranked as "Hard" and
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