In each of the following letter series, some of the letters are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.

_ _aba _ _ ba _ ab

Answer: Option B

Explanation:

The series is ab/ab/ab/ab/ab/ab. Thus, the pattern 'ab' is repeated.

c _ bbb _ _ abbbb _ abbb _

The series is cabbbb/cabbbb/cabbbb. Thus, the pattern 'cabbbb' is repeated.

_ bbca _ bcca _ ac _ a _ cb

The series is abbc/ac/bcca/ba/caab/cb.

a _ bbc _ aab _ cca _ bbcc

The series is aabbcc/aabbcc/aabbcc. Thus, the pattern 'aabbcc' is repeated.

ac _ cab _ baca _ aba _ acac

Answer: Option A

The series is acac/abab/acac/abab/acac. Thus, the pattern acac/abab is repeated