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 letter + 5 = 3rd letter and 2nd letter - 5 = 4th letter

Now, we check each options.

Option (a): OR – TN (Not Follow)​

O + 5 = T, R - 5 $$\neq$$​ N

Option (b): JM – OH (Follow)

J + 5 = O, M - 5 = H

Option (c): SV – XQ (Follow)​

S + 5 = X, V - 5 = Q

Option (d): BE – GZ (Follow)​

B + 5 = G, E - 5 = Z

Thus, correct option is (a).