Correct Answer: abbaaba

Solution : Given:
_b_baaabb_a_ _bb_a_

To fill the series we have to divide the series – _b_ / baa / abb / _a_ / _bb / _a_

Let's check each option –
First option: abbaaba; a b b / baa / abb / b a a / a bb / b a a (abb and baa is the alternate repeated pattern in the series)
Second option: ababbaa; a b b / baa / abb / a a b / b bb / a a a (No repeated pattern has been found)
Third option: babaaba; b b a / baa / abb / b a a / a bb / b a a (No repeated pattern has been found)
Fourth option: baabaab; b b a / baa / abb / a a b / a bb / a a b (No repeated pattern has been found)

So, the series becomes→abbbaaabbbaaabbbaa. Hence, the first option is correct.