Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.

g _o_ d k _ m _f _ o _ k k _ g f o _ d _ k m

f o k g o d m o k 

g _o_ d k _ m _f _ o _ k k _ g f o _ d _ k m

The logic followed here is :

g f o o d k k m - g f o o d k k m - g f o o d k k m

Here ( g f o o d k k m ) is repeated

Therefore ' f o k g o d m o k' is correct answer