Step-by-step Solution:

The one which is different from the other three is JGP.

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The Pattern Breakdown

The logic in this puzzle is based on a consistent pattern of shifts in the alphabet. Three of the options follow the same rule, while one does not.

1. The Rule: The pattern is that the second letter is 3 positions before the first letter, and the third letter is 8 positions after the second letter. (A -3, +8 pattern).
2. Applying the Rule:
   • HEM: H (8) → E (5) is -3. E (5) → M (13) is +8.
   • NKS: N (14) → K (11) is -3. K (11) → S (19) is +8.
   • OLT: O (15) → L (12) is -3. L (12) → T (20) is +8.
3. The Odd One Out:
   • JGP: J (10) → G (7) is -3. However, G (7) → P (16) is +9.

Since JGP follows a (-3, +9) pattern, it is the one that is different from the other three.