In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
c _ bba _ cab _ ac _ ab _ ac
_ aaba _ bba _ bba _ abaa _ b
_ bcc _ ac _ aabb _ ab _ cc
ac _ cab _ baca _ aba _ acac
b _ ac _ cc _ cb _ ab _ ac
_ bbca _ bcca _ ac _ a _ cb