Explanation
The series is formed by repeating a five-letter pattern where the first four letters remain relatively constant as KOCT, while the fifth letter follows an alphabetical or repetitive progression. The series can be divided into groups of five letters as follows:
First Group (1-5): K O C T Q
The first blank is at the second position. Filling it with O from the first letter of the option gives K O C T Q.
Second Group (6-10): K O C T R
The blanks are at the sixth, ninth, and tenth positions. Filling them with K, T, and R from the option gives K O C T R.
Third Group (11-15): K O C S T
The fixed letters in the series are K, O (at 11, 12) and T (at 15). The blanks are at the thirteenth and fourteenth positions. Filling them with C and S from the option gives K O C S T.
Fourth Group (16-20): K O C T T
The seventh letter of the option, C, fits into the third position of the subsequent repeating block, maintaining the sequence.
By sequentially placing the letters O, K, T, R, C, S, and C into the blanks, the series completes a logical progression: KOCTQ, KOCTR, KOCST, KOCTT. This pattern of a fixed prefix with a shifting or incrementing suffix is a standard logic in letter series puzzles.