Which of the following groups of letters when sequentially placed from left to right will complete the given series?
dddeeeff_dddeeeff_dddeeefffdddee_ff_

Correct option is C

Given: dddeeeff_dddeeeff_dddeeefffdddee_ff_
(a) fdef → dddeeeff f/dddeeeff/ ddddeeefffdddee eff f (Sequence not followed.)
(b) fded → dddeeeff f/dddeeeff/ ddddeeefffdddee eff d (Sequence not followed.)
(c) ffef → dddeeeff f/dddeeeff f/dddeeefff/dddee eff f (Sequence followed.)
(d) edfd → dddeeeff edddeeeff ddddeeefffdddee fff d (Sequence not followed.)
Correct answer is (c) ffef.