Select the option that represents the letters that, when sequentially placed from left to right in the blanks below, will complete the letter series.

r d _ n _ d r _ _ b n n d _ r d b _ n d r

b n r d r n

After dividing it into groups  and comparing the corresponding term we, get "b n r d r n" as the repetitive term because it follows the pattern.

r d b n n d r rd b n n d r r d b n n d r