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 - 3 = 3rd letter and 2nd letter - 3 = 4th letter
Now, we check each options.
​Option (a): PS - MP (Follow)

P - 3 = M, S - 3 = P
​Option (b): GJ - DG (Follow)​

G - 3 = D, J - 3 = G
​Option (c): EH - BE (Follow)​

E - 3 = B, H - 3 = E
​Option (d): RK - JH (Not Follow)​

R - 3 $$\neq$$​ J, K - 3 = H
Thus, correct option is (d). ​​