Number Series - Verbal and Reasoning

Directions to SolveLook carefully for the pattern, and then choose which pair of numbers comes next.
Q1:

8 11 21 15 18 21 22

A 25 18

B 25 21

C 25 29

D 24 21

E 22 26

ANS:B - 25 21

This is an alternating addition series, with a random number, 21, interpolated as every third number. The addition series alternates between adding 3 and adding 4. The number 21 appears after each number arrived at by adding 3.