Letter Series

JAK, KBL, LCM, MDN, ?

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

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

What should come next in the series: Z,X,U,Q,L,...

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

In 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:
a _ a _ b _ _ acb _ _ acb

P3C, R5F, T8I, V12L, X17O, ?

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:
_ _ babbba _ a _ _

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