Letter Series

In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative:
_ _ aba _ _ ba _ ab

Find the term which continues the letter series:
AKU, FPZ,……, PZJ, UEO, ZJT

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

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: 
aab _ aa _ bbb _ aaa _ bbb

Choose the correct option to complete the alphabet series:
ba _ cb _ b _ bab _

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

PLD , QJG, RHJ, SFM, TDP, ?

GMQ, JOT, MQW, ?

BV, CU, ES, HP, LL, QG, ?

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