Select the combination of letters that when sequentially placed in the gaps of the given letter series will complete the series.
H _ _ E P C K _ _ C D E P _ K F H C _ E P C _ F

By Trial and Error method,

Option A

H D C E P C K F | H C D E P F K F | H C D E P C D F

The above letters do not form a series. Hence option A is incorrect.

Option B

H C D E P C K H | H C D E P D K F | H C C E P C K F

The above letters do not form a series. Hence option B is incorrect.

Option C

H C C E P C K F | H C D E P K K F | H C D E P C K F

The above letters do not form a series. Hence option C is incorrect.

Option D

H C D E P C K F | H C D E P C K F | H C D E P C K F

The above letters form a series.

Hence, the correct answer is Option D