Series Completion - Verbal and Reasoning

Directions to SolveIn 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.
Q1:

ab _ aa _ bbb _ aaa _ bbba

A abba

B baab

C aaab

D abab

ANS:B - baab

Explanation: The series is abb/aaabbb/aaaabbbb/a. Thus the letters are repeated twice, then thrice, then four times and so on.