Based on the English alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Which letter-cluster does not belong to that group?
(Note: The odd letter-cluster is not based on the number of consonants/vowels or their position in the letter-cluster.)

To identify the letter-cluster that does not belong to the group, we analyze the positions of the letters in each cluster according to the English alphabetical order (where A = 1, B = 2, ..., Z = 26). Let's determine the differences between the consecutive letters in each option:

1. For FIK:
The alphabetical positions are:
F = 6, I = 9, K = 11
Let's find the differences between consecutive letters:
F to I: 9 - 6 = +3
I to K: 11 - 9 = +2
The pattern is +3, +2.

2. For ORT:
The alphabetical positions are:
O = 15, R = 18, T = 20
Let's find the differences:
O to R: 18 - 15 = +3
R to T: 20 - 18 = +2
The pattern is +3, +2.

3. For DGI:
The alphabetical positions are:
D = 4, G = 7, I = 9
Let's find the differences:
D to G: 7 - 4 = +3
G to I: 9 - 7 = +2
The pattern is +3, +2.

4. For JMP:
The alphabetical positions are:
J = 10, M = 13, P = 16
Let's find the differences:
J to M: 13 - 10 = +3
M to P: 16 - 13 = +3
The pattern is +3, +3.

We can clearly see that FIK, ORT, and DGI follow the pattern where the letters increase by +3 and then by +2. On the other hand, JMP follows the pattern of +3 and +3. Therefore, JMP does not belong to the group.

The correct answer is JMP.