1.  In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative : ab _ aa _ bbb _ aaa _ bbba

A. abba
B. baab
C. aaab
D. abab

Answer: Option B

Explanation:

The series is abb / aaabbb / aaaabbbb / a.

Thus, the letters are repeated twice, then thrice, then four times and so on.