Find the next three terms of the sequence.
3, 6, 9, 12, . . .
A. 15, 18, 20
B. 15, 19, 21
C. 15, 18, 21
D. 14, 18, 21
The common difference between the terms is 3, so the next three terms are:
15, 18, 21
Therefore, the answer is (C) 15, 18, 21.