Since this question asks which of the following CANNOT be true, you will likely be able to disprove most (if not all) of the wrong answers with some simple examples. If we can prove that an answer IS possible (even just once), then we can eliminate it.
We're told that (A-B)(C) < 0
This means that one of the two parentheses MUST be POSITIVE while the other MUST be NEGATIVE. Recognizing THIS Number Property should speed you up - You can now either TEST VALUES or use this Number Property to eliminate answers.
Answer A: A < B
If A<B, then (A-B) is negative and C is positive. This IS possible. Eliminate A.
Answer B: C < 0
IF C<0, then (A-B) is positive. This IS possible. Eliminate B.
Answer C: |C| < 1
C can be positive or negative, so (A-B) would be the opposite. This IS possible. Eliminate C.
Between the remaining two answers, Answer E seems like the easier option to eliminate....
Answer E: A^2 - B^2 > 0
IF A>B and they're both positive, then (A-B) is positive and C is negative. This IS possible. Eliminate E.
There's only one answer left....
GMAT assassins aren't born, they're made,
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