Select the combination of letters that when sequentially placed in the gaps of the given letters series will complete the series.
b_bab_bc_abbb_ba_b

Find the missing number.
25, 121, 361, 1369, ?

Which one set of letters when sequentially placed at the gaps in the given letter series shall complete it.
c_bba_cab_ac_ab_ac

Which one set of letters when sequentially placed at the gaps in the given letter series shall complete it.
deb, ijg, nol ? xyv

11 , 13 , 17 , 19 , 23 , 25 , ?

What will come in place of question (?) mark in the following series?
CD     FG     JK     ?        UV

Which of the following groups of alphabets should replace the blank spaces so that the group of alphabets, given in bold, follow a logical pattern from the preceding and the following group of alphabets?
b w_ y z a   d s t u v _   _o p q r e

20, 21, 19, 16, 17, 13, 14, 11, ?