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If you guess, choose A,C or E. Don't repeat a letter (if guessing).I read a book about guessing for these tests and you know what you know, but the ones you don't know can make or break it, so the book gave the above suggestions (I'm oversimplifying it).
On the GRE, they rather you answer, because you get more points deducted for skipped questions than for guessing.~Marti