Which of the following is a geometric series?

A geometric series has a constant ratio between consecutive terms. In choice B, each term is multiplied by 3: 3 ÷ 1 = 3, 9 ÷ 3 = 3, and 27 ÷ 9 = 3. Therefore, 1 + 3 + 9 + 27 is geometric. The other choices do not have a constant ratio.

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