Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.
G _ _ D O _ K N _ O G K _ D _ G K _ _ O
A) K N D G N O N D
B) K N G N D O N D
C) K N G D N O G D
D) K N G D N O N D

Let's check the total length of the series, which is 20 letters. Let's test the option pattern by creating equal blocks of 5:
G _ _ D O | _ K N _ O | G K _ D _ | G K _ _ O

Let's try Option D: K N G D N O N D
Placing the letters sequentially in the blanks:

K

N

G

D

N

O

N

D

The sequence becomes:
G K N D O | G K N D O | G K N D O | G K N D O

This forms a perfect repeating pattern of the 5-letter word G K N D O.