Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
HDMS, OVVI, VNEY, CFNO, ?

The correct answer is JXWE.

To solve this, we analyze each of the four letter positions independently across all five clusters in the series:

Series: HDMS, OVVI, VNEY, CFNO, ?

Position 1 (1st letter of each cluster): H, O, V, C, ?

Converting to numerical values (A=1, B=2, ... Z=26):

H = 8, O = 15, V = 22, C = 3

Differences: 15 - 8 = +7, 22 - 15 = +7, 3 - 22 = -19, but in a circular alphabet (mod 26): 22 + 7 = 29 → 29 - 26 = 3 = C ✓

So the pattern is +7 each step (circular).
Next: C(3) + 7 = 10 = J

Position 2 (2nd letter of each cluster): D, V, N, F, ?

D = 4, V = 22, N = 14, F = 6

Differences (mod 26): 4 + 18 = 22 ✓, 22 + 18 = 40 → 40 - 26 = 14 ✓, 14 + 18 = 32 → 32 - 26 = 6 ✓

So the pattern is +18 each step (circular).
Next: F(6) + 18 = 24 = X

Position 3 (3rd letter of each cluster): M, V, E, N, ?

M = 13, V = 22, E = 5, N = 14

Differences: 13 + 9 = 22 ✓, 22 + 9 = 31 → 31 - 26 = 5 ✓, 5 + 9 = 14 ✓

So the pattern is +9 each step (circular).
Next: N(14) + 9 = 23 = W

Position 4 (4th letter of each cluster): S, I, Y, O, ?

S = 19, I = 9, Y = 25, O = 15

Differences: 9 - 19 = -10, 25 - 9 = +16, 15 - 25 = -10

The pattern alternates: -10, +16, -10, +16, ...
The 4th difference was -10, so the 5th follows +16... wait — let's recount: step 1→2 = -10, step 2→3 = +16, step 3→4 = -10. So step 4→5 = +16? But that gives 15+16=31→5=E.
Actually let's verify with -10: the alternation is (-10, +16, -10, +16...). The 4th step (3→4) used -10, so step (4→5) uses +16? 15+16=31→31-26=5=E. Hmm. Let's try consistently -10: 19-10=9✓, 9-10=-1→25✓(mod 26: -1+26=25), 25-10=15✓. So the pattern is actually a consistent -10 (mod 26)!
Next: O(15) - 10 = 5 = E

Combining all four positions:

Position 1 → J
Position 2 → X
Position 3 → W
Position 4 → E

The missing cluster is JXWE.