Find the missing letters:

Z, W, S, P, L, I, E, ?

Find the missing letters:

B, E, I, N, T, ?

Find the missing letters:

A D, D I, I P, P ? 

Find the missing letters :

ab _ ba_ ba_

Find the missing letters in the given sequence below:

abaa_ aab_ a _ a

Find the missing letters:

aa_ b_ abb_ _ bb

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

a_ ab_ baa_ bb_ 

Find the missing letters :

abc_ be_ c_

Find the missing letters :

aabc__bca_b_a_bc