Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
BDH, EJM, IPR, ?

The correct option is NVW.

To find the missing letter-cluster that replaces the question mark (?), let us analyze the pattern of the letters at each position across the series: BDH, EJM, IPR, ?

First, consider the alphabetical positions of each letter:
B = 2, D = 4, H = 8
E = 5, J = 10, M = 13
I = 9, P = 16, R = 18

Now, let us examine the pattern for each letter position separately:

1. First letter of each cluster:
B (2) → E (5): +3
E (5) → I (9): +4
Following the pattern (+3, +4, ...), the next step should be +5:
I (9) + 5 = 14, which corresponds to the letter N.

2. Second letter of each cluster:
D (4) → J (10): +6
J (10) → P (16): +6
The pattern is a constant addition of 6:
P (16) + 6 = 22, which corresponds to the letter V.

3. Third letter of each cluster:
H (8) → M (13): +5
M (13) → R (18): +5
The pattern is a constant addition of 5:
R (18) + 5 = 23, which corresponds to the letter W.

Combining the resulting letters from each position gives NVW.

Therefore, the letter-cluster that replaces the question mark is NVW.