In alphabet series, some alphabets are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.
ab _ aa _ bbb _ aaa _ bbba
ab _ _ _ b_ bbaa _
ab _ bcbca _ _ c _ bab
ab _ aa _ caab _ c _ abb _ c
c _ bbb _ _ abbbb _ abbb _
b _ b _ bb _ _ bbb _ bb _ b