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 _ baca _ ba _ bacaabac _ aca
_ abb _ _ bb _ a _ bbab _ ba
_ _ aba _ _ ba _ ab
a _ cacbc _ baca _ _ b
ac _ cab _ baca _ aba _ acac
ab _ bc _ c _ ba _ c