Letter series type of questions usually consists of a series of small letters which follow a certain pattern. However, some letters are missing from the series. These missing letters are then given in a proper sequence as one of the alternatives. The candidate is requitred to choose this alternative as the answer.
In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
abb _ baa _ a _ bab _ aba
Answer: A . abba
The series is abba / baab / abba / baab / a.
Thus, the pattern abba, baab is repeated.