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.

c__bba__cab__ac__ab__ac
A. bcacb
B. babcc
C. abcbc
D. acbcb

Answer: Option D

Explanation:

Pattern of the series as shown below

cab/bac/cab/bac/cab/bac => acbcb

The sequence is made of repetition of two patterns cab and bac alternatively

Hence, the missing letters are acbcb.