Select the option that is related to the third letter-cluster in the same way as the second letter-cluster is related to the first letter-cluster.

RS : QT :: AK : ?

IC

A   B   C    D   E    F   G    H    I    J    K    L   M

 ↓    ↓    ↓    ↓    ↓     ↓   ↓    ↓     ↓   ↓    ↓    ↓    ↓

 Z   Y    X   W   V    U   T    S    R   Q   P    O   N

26  25  24  23  22  21  20  19  18  17  16  15  14

******************************************

RS : QT :: AK : ?

The  logic followed here is :

R → (+2) → T

S → (-2) → Q

TQ → WRITTEN IN BACKWARD FORM → QT

SIMILARLY

A → (+2) → C

K → (-2) → I

CI → WRITTEN IN BACKWARD FORM → IC