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 one that DOES NOT belong to that group?

Logic: 1st letter - 2 = 3rd letter and 2nd letter - 2 = 4th letter

Now, we check each options.

Option (a): BW : ZU (Follow)

B - 2 = Z, W - 2 = U

Option (b): HC : FA (Follow)

H - 2 = F, C - 2 = A

Option (c): EZ : DX (Not follow)

E - 2 $$\ne$$ D, Z - 2 = X

Option (d): UP : SN (Follow)

U - 2 = S, P - 2 = N

Thus, correct option is (c).