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 + 2 = 3rd, 2nd + 2 = 4th

a). IM - KO

I + 2 = K

M + 2 = O

b). SP - QI

S + 2 = U ≠ Q

P + 2 = R ≠ I

d). LP - NR

L + 2 = N

P + 2 = R

d). GK - IM

G + 2 = I

K + 2 = M

Thus, correct option is (b).

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