What should come in place of the question mark (?) in the given series based on the English alphabetical order?
MKH, PNK, SQN, VTQ, ?

The correct option is YWT.

Let us analyze the given letter-cluster series based on the positions of the letters in the English alphabetical order:

Given series:
MKH, PNK, SQN, VTQ, ?

Let us break down each letter-cluster by analyzing the pattern for each position across the series:

1. First letters:
M → P → S → V → ?

Using alphabetical positions:
M (13) + 3 = P (16)
P (16) + 3 = S (19)
S (19) + 3 = V (22)
V (22) + 3 = Y (25)

So, the first letter is Y.

2. Second letters:
K → N → Q → T → ?

Using alphabetical positions:
K (11) + 3 = N (14)
N (14) + 3 = Q (17)
Q (17) + 3 = T (20)
T (20) + 3 = W (23)

So, the second letter is W.

3. Third letters:
H → K → N → Q → ?

Using alphabetical positions:
H (8) + 3 = K (11)
K (11) + 3 = N (14)
N (14) + 3 = Q (17)
Q (17) + 3 = T (20)

So, the third letter is T.

Combining all three positions, the letter-cluster that replaces the question mark (?) is YWT.