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.
MEK: NVP :: GYT : TBG :: JWH:?

The correct option is QDS.

To solve this letter-cluster analogy, we need to determine the relationship between the letters in each pair of clusters. Let's analyze the alphabetical positions of the letters (where A = 1, B = 2, ..., Z = 26) and look for a pattern.

The relationship between the first and second letter-clusters is based on opposite letters in the alphabet. Two letters are opposites if the sum of their numerical positions is 27:

$\text{Opposite Position}=\; 27\; -\text{Original Position}$

1. Analyzing the first pair: MEK : NVP
For M (13th letter):
$27\; -\; 13\; =\; 14$, which corresponds to N.
For E (5th letter):
$27\; -\; 5\; =\; 22$, which corresponds to V.
For K (11th letter):
$27\; -\; 11\; =\; 16$, which corresponds to P.
Thus, MEK becomes NVP.

2. Analyzing the second pair: GYT : TBG
For G (7th letter):
$27\; -\; 7\; =\; 20$, which corresponds to T.
For Y (25th letter):
$27\; -\; 25\; =\; 2$, which corresponds to B.
For T (20th letter):
$27\; -\; 20\; =\; 7$, which corresponds to G.
Thus, GYT becomes TBG.

3. Applying the same logic to the fifth letter-cluster: JWH : ?
For J (10th letter):
$27\; -\; 10\; =\; 17$, which corresponds to Q.
For W (23rd letter):
$27\; -\; 23\; =\; 4$, which corresponds to D.
For H (8th letter):
$27\; -\; 8\; =\; 19$, which corresponds to S.
Thus, the corresponding cluster is QDS.