Correct Answer: bbaa

Solution : Given:

_ aabab_ab_ab_bba

Let's check the given options –

First option: bbaa

The series becomes b aabab b ab a ab a bba

The pattern in the series becomes b aabab b a / b a ab a bba

Second option: baaa

The series becomes b aabab a ab a ab a bba

There is no pattern in the above series.

Third option: abaa

The series becomes a aabab b ab a ab a bba

There is no pattern in the above series.

Fourth option: abba

The series becomes a aabab b ab b ab a bba

There is no pattern in the above series.

Hence, the first option is correct.