Which one number will complete the series: 8, 13,10, 15, 12,17, 14, …..?

A) 19

B) 22

C) 16

D) 20

When given series is increasing as well as decreasing, there are two series:

1st Series               2nd Series 

8 +2 =10                 13 + 2=15

10 + 2= 12               15 + 2 =17

12 + 2=14                17+2 =19