Which letter-pair will replace the question mark (?) in the following series?
KH, ? , QN, WT, EB

The difference between first letter of each letter pair is even number series as shown below

M-K = 13-11 = 2

Q-M = 17-13 = 4

W-Q = 23-17 = 6

E-W = 31-23 = 8

$$=$$>   The first letter of the second letter-pair is M

The difference among the letters of the letter-pairs is 3 as shown below

K-H = 11-8 = 3

M-J = 13-10 = 3

Q-N = 17-14 = 3

W-T = 23-20 = 3

E-B = 5-2 = 3

$$=$$>  The second letter of the second letter-pair is J

Hence, the correct answer is Option B