Correct Answer: c b b a a

Solution : Given -

adb _ ac _ da _ cddcb _ dbc _ cbda

Let's check the options.

option first: b c c b a

The series becomes adb b ac c da c cddcb b dbc a cbda

There is no pattern in the above series.

option second: c c b b a

The series becomes adb c ac c da b cddcb b dbc a cbda

There is no pattern in the above series.

option third: c b b a a

The series becomes adb c ac b da b cddcb a dbc a cbda

The pattern in the series becomes adbc/acbd/abcd/dcba/dbca/cbda.

option fourth: b b c a d

The series becomes adb b ac b da c cddcb a dbc d cbda

There is no pattern in the above series.

Hence, third option is correct.