In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
_ _ aba _ _ ba _ ab
abb _ baa _ a _ bab _ aba
_ abb _ _ bb _ a _ bbab _ ba
_ aba _ cabc _ dcba _ bab _ a
_ baa _ aab _ a _ a
aba _ baca _ ba _ bacaabac _ aca