Correct Answer: bbabb

Solution : Given:
a _ ba _ b _ b _ a _ b

To fill the series we have to divide the series→ a _ b / a _ b / _ b _ / a _ b
Let's check each option –
First option: abaab; a a b / a b b / a b a / a b b (No repeated pattern has been found.)
Second option: aabba; a a b / a a b / b b b / a a b (No repeated pattern has been found.)
Third option: bbabb; a b b / a b b / a b b / a b b (abb is repeated in the series.)
Fourth option: abbab; a a b / a b b / b b a / a b b (No repeated pattern has been found.)

So, the series becomes→abbabbabbabb. Hence, the third option is correct.