In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
aa _ aaa _ aaaa _ aaaa _ b
abb _ baa _ a _ bab _ aba
_ abb _ _ bb _ a _ bbab _ ba
ba _ b _ aabb _ a _ _ a _ bb
_ _ aba _ _ ba _ ab
_ _ babbba _ a _ _