1. 

In the following question, a letter series is given. Some of the letters of the series are missing. This missing letters are given in same order as one of the four/five alternatives below the series. Find out the correct alternative.

__b__baaabb__a__ __bb__a__
A. abbaaba
B. ababbaa
C. babaaba
D. baabaab

Answer: Option A

Explanation:

Pattern of the series as shown below

abb/baa/abb/baa/abb/baa => abbaaba

The series is repetition of alternative two blocks 'abb' and 'baa'.

Hence, the missing letters are abbaaba.