ExplanationSince a positive multiple must be greater than or equal to the number it is a multiple of, answer choice (C) cannot be a multiple of a or b, as it is smaller than both integers a and b.
Alternatively, try testing numbers such that a is larger than b:
(A) If a = 3 and b = 2, a – 1 = 2, which is a multiple of b.
(B) If a = 3 and b = 2, b + 1 = 3, which is a multiple of a.
(C) Is the correct answer by process of elimination.
(D) If a = 4 and b = 2, a + b = 6, which is a multiple of b.
(E) If a = 3 and b = 2, ab = 6, which is a multiple of both a and b.
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