In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
_ baa _ aab _ a _ a
abb _ baa _ a _ bab _ aba
aa _ ab _ _ aaa _ a
_ abb _ _ bb _ a _ bbab _ ba
c _ baa _ aca _ cacab _ acac _ bca
_ bc _ _ bb _ aabc