Which of the following is an arithmetic sequence?

1/2, 2, 7/2, 5

The differences between adjacent terms of an arithmetic sequence are the same.

No sequence in which signs alternate can be an arithmetic sequence. This eliminates the 1st and 4th choices.

The denominators of the 2nd sequence are an arithmetic sequence, meaning that sequence is a "harmonic" sequence, not an arithmetic one. The differences between adjacent terms get smaller and smaller. They are not a constant.

Differences between terms of the 3rd sequence are all 3/2. This is your arithmetic sequence.

your answer is C: 1/2, 2, 7/2, 5...