Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
YMW, VJT, SGQ, PDN, ?

The correct option is MAK.

To find the missing letter-cluster in the given series, let us analyze the pattern followed by each letter position across the sequence: YMW, VJT, SGQ, PDN, ?

First Letter Pattern:
Y (25) - 3 = V (22)
V (22) - 3 = S (19)
S (19) - 3 = P (16)
P (16) - 3 = M (13)

Second Letter Pattern:
M (13) - 3 = J (10)
J (10) - 3 = G (7)
G (7) - 3 = D (4)
D (4) - 3 = A (1)

Third Letter Pattern:
W (23) - 3 = T (20)
T (20) - 3 = Q (17)
Q (17) - 3 = N (14)
N (14) - 3 = K (11)

Combining all the derived letters, we get the letter-cluster MAK.