Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
BDHJ, CEIK, DFJL, EGKM, ?

The correct option is FHLN.

To find the missing letter-cluster that replaces the question mark (?), let's analyze the pattern by observing the position of each letter in the English alphabet for every term in the given series.

Step 1: Analyze the first letter of each cluster
B (2) ⇒ C (3) ⇒ D (4) ⇒ E (5) ⇒ ?
The pattern increases by +1 each time. Therefore, the next letter is F (6).

Step 2: Analyze the second letter of each cluster
D (4) ⇒ E (5) ⇒ F (6) ⇒ G (7) ⇒ ?
The pattern increases by +1 each time. Therefore, the next letter is H (8).

Step 3: Analyze the third letter of each cluster
H (8) ⇒ I (9) ⇒ J (10) ⇒ K (11) ⇒ ?
The pattern increases by +1 each time. Therefore, the next letter is L (12).

Step 4: Analyze the fourth letter of each cluster
J (10) ⇒ K (11) ⇒ L (12) ⇒ M (13) ⇒ ?
The pattern increases by +1 each time. Therefore, the next letter is N (14).

Combining all the letters together, we get FHLN.