Based on the English alphabetical order, three of the following four letter-cluster pairs are alike in a certain way and thus form a group. Which is the letter-cluster pair that DOES NOT belong to that group?
(Note: The odd one out is not based on the number of consonants/vowels or their position in the letter-cluster.)

​Logic: 1st - 8 = 3nd,  2nd -9 = 4th

a) NK–FG

N – 8 → F
K – 9 → B ≠ G

b) IF–AW
I – 8 → A
F – 9 → W

c) UR–MI
U – 8 → M
R – 9 → I

d) BY–TP
B – 8 → T
Y – 9 → P

Odd one out: D. BY–TP