Correct Answer: mabam

Solution : Given:
_bbm_amb_m_a_bbm

To fill the series we have to divide the series – _ / bb / m / _a / m / b_ / m / _a / _ / bb / m
Let's check the option –
First option: mbabm; m / bb / m / b a / m / b a / m / b a / m / bb / m (No repeated pattern has been found.)
Second option: ambbm; a / bb / m / m a / m / b b / m / b a / m / bb / m (No repeated pattern has been found.)
Third option: mabam; m / bb / m / a a / m / b b / m / a a / m / bb / m (In every alternate part starting from first m is repeated; In every alternate part starting from second bb changes to aa and then aa changes to bb)
Fourth option: abmab; a / bb / m / b a / m / b m / m / a a / b / bb / m (No repeated pattern has been found.)

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