Letter Series

In following questions, a sequence of groups of alphabets is provided with one term missing , Choose the missing term from options: 
A, CD, GHI, ?, UVWXY

In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative: 
a _ bbc _ aab _ cca _ bbcc

GMQ, JOT, MQW, ?

JAK, KBL, LCM, MDN, ?

In following question, a sequence of groups of alphabets is provided with one term missing , Choose the missing term from options:
AB, DEF, HIJK, ?, STUVWX

In each of the following letter series, some of the letters are missing which are given in that order as one of the alternatives below it. Choose the correct alternative:
cccbb _ aa _ cc _ bbbaa _ c

In the following alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative:
abb _ baa _ a _ bab _ ab

P3C, R5F, T8I, V12L, X17O, ?

LXF, MTJ, NPN, OLR, ?

LRX, DJP, VBH, NTZ, ?