9, 12, 11, 14, 13, 16, 15, ... choose which pair of numbers comes next?

A 14, 13

B 18, 21

C 14, 17

D 12, 13

E 18, 17

Correct Answer: Option E

This is a simple alternating addition and subtraction series. First, 3 is added, then 1 is subtracted, then 3 is added, 1 subtracted, and so on.