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