Letter Series

What should come next in the series: T,R,P,N,...

QAR, RAS, SAT, TAU, ?

ZEA, WFB, TGD, QHG, ?

In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative: 
abca _ bcaab _ ca _ bbc _

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

Choose the correct option to complete the letter series:
ab _ _ baa _ _ ab _

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

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