Correct Answer: abca

Solution : Given:

_bcab_cabc_abca_b

Let's check the given options –

First option: abac

The series becomes a bcab b cabc a abca c b

There is no pattern in the above series.

Second option: abca

The series becomes a bcab b cabc c abca a b

The pattern in the series becomes a bcab / b cabc / c abca / a b

Third option: aabc

The series becomes a bcab a cabc b abca c b

There is no pattern in the above series.

Fourth option: baaa

The series becomes b bcab a cabc a abca a b

There is no pattern in the above series.

Hence, the second option is correct.