Select the option that is related to the fifth letter-cluster in the same way as the second letter-cluster is related to the first letter-cluster and the fourth letter-cluster is related to the third letter-cluster.
JOCK : GLZH :: HURT : EROQ :: SPIN : ?

To find the letter-cluster that is related to "SPIN" in the same way as the other pairs, let's analyze the pattern or rule governing the relationships between the first two pairs: JOCK : GLZH and HURT : EROQ.

First, let's look at the first pair: JOCK : GLZH.
We examine the transition from each letter in the first cluster (JOCK) to the corresponding letter in the second cluster (GLZH) by looking at their positions in the English alphabet (where A = 1, B = 2, ..., Z = 26):
1. First letter: J (10) → G (7). The change is:
$\mathrm{10}-3=7$ (G)
2. Second letter: O (15) → L (12). The change is:
$\mathrm{15}-3=\mathrm{12}$ (L)
3. Third letter: C (3) → Z (26). Moving backwards by 3 from C (C → B → A → Z) gives:
$3-3=0\equiv \mathrm{26}$ (Z)
4. Fourth letter: K (11) → H (8). The change is:
$\mathrm{11}-3=8$ (H)
Thus, the rule is to subtract 3 from the alphabetical position of each letter (or shift 3 positions backward: -3, -3, -3, -3).

Now, let's verify this rule with the second pair: HURT : EROQ.
1. First letter: H (8) → E (5). The change is:
$8-3=5$ (E)
2. Second letter: U (21) → R (18). The change is:
$\mathrm{21}-3=\mathrm{18}$ (R)
3. Third letter: R (18) → O (15). The change is:
$\mathrm{18}-3=\mathrm{15}$ (O)
4. Fourth letter: T (20) → Q (17). The change is:
$\mathrm{20}-3=\mathrm{17}$ (Q)
The pattern is confirmed to be subtracting 3 from each letter's alphabetical position.

Now, we apply this same pattern (-3, -3, -3, -3) to the fifth letter-cluster: SPIN.
1. First letter: S (19) → 19 - 3 = 16, which is P.
2. Second letter: P (16) → 16 - 3 = 13, which is M.
3. Third letter: I (9) → 9 - 3 = 6, which is F.
4. Fourth letter: N (14) → 14 - 3 = 11, which is K.

Combining these letters, we get the related letter-cluster: PMFK.

Therefore, the correct option is PMFK.