Correct Answer: ABABCBBAB

Solution : Given:
A_ _BCD_AB_ _DAA_ _CDA_ _BCD

To fill the series we have to divide the series –
A_ _BCD \ _AB_ _D \ AA_ _CD \ A_ _BCD

Let's check each option –
First option: ACBBABBAB; A AC BCD \ B AB BA D \ AA BB CD \ A AB BCD (No repeated pattern has been found)
Second option: ABABCBBAB; A AB BCD \ A AB BC D \ AA BB CD \ A AB BCD (AABBCD is repeated in the series)
Third option: ABBBABCAB; A AB BCD \ B AB BA D \ AA BC CD \ A AB BCD (No repeated pattern has been found)
Fourth option: BABABABCB; A BA BCD \ B AB AB D \ AA AB CD \ A CB BCD (No repeated pattern has been found)

Thus, the series becomes – AABBCDAABBCDAABBCDAABBCD. Hence, the second option is correct.