Which of the following is an arithmetic sequence?

An arithmetic sequence has the same difference between every pair of consecutive terms. In choice D, the differences are 2 − 1/2 = 3/2, 7/2 − 2 = 3/2, and 5 − 7/2 = 3/2. Since the difference is constant, the sequence 1/2, 2, 7/2, 5 is arithmetic.

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