Correct Answer: abbb

Solution : Given:

b_ab_b_aab_b

Let's check the given options –

First option: aabb

The series becomes b a ab a b b aab b b

There is no pattern in the above series.

Second option: abbb

The series becomes b a ab b b b aab b b

The pattern in the series becomes b a ab b b / b aab b b

Third option: abba

The series becomes b a ab b b b aab a b

There is no pattern in the above series.

Fourth option: baaa

The series becomes b b ab a b a aab a b

There is no pattern in the above series.

Hence, the second option is correct.