GMAT Sentence Correction (SC) | Re: Prices at the producer level are only 1.3 percent higher now

The simple answer is that the GMAT is not consistent on this. Keep in mind that comma usage is generally not tested directly. The one absolute rule you *can* rely on is that you can't join two independent clauses with *only* a comma, as in "I like pie, it is tasty." You always need a conjunction or a semicolon.

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