UGC,OLD QUESTION: Complete the following series9,11,15,23,39, ______?

Complete the following series
9,11,15,23,39, ______?

A 71
B 65
C 44
D 68

Answer :A 

71 is the answer

9+2=11

11+4=15

15+8=23

23+16=39

39+32=71.

(2+2=4, 4+4=8, 8+8=16,16+16=32, )