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 letter-cluster pair 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 + 6 = 3rd, 2nd - 3 = 4th

Option A: TX → ZV

T + 6 → Z
X – 2 → V

Option B: HL → NI

H + 6 → N
L – 3 → I

Option D: MQ → SN

M + 6 → S
Q – 3 → N

Option C: CG → ID

C + 6 → I
G – 3 → D

Thus, the correct option is (a).