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

ACE : IKM :: QSU : ?

YAC

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

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

ACE : IKM :: QSU : ?

The  logic followed here is :

A → (+8) → I

C → (+8) → K

E → (+8) →M

SIMILARLY

Q → (+8) → Y

S → (+8) → A

U → (+8) → C