Select the letter-cluster that can replace the question mark (?) in the following series.
OQS, ?, ACE, GIK, MOQ

Correct option is B

Given series: OQS, ?, ACE, GIK, MOQ
The pattern is +6
OQS: O (15), Q (17), S (19)
ACE: A (1), C (3), E (5)
GIK: G (7), I (9), K (11)
MOQ: M (13), O (15), Q (17)
Now, applying the logic of +6 for each letter:
From OQS to the missing term:
O (15) + 6 = U (21)
Q (17) + 6 = W (23)
S (19) + 6 = Y (25)
Thus, the missing term is UWY.
Correct answer is (b) UWY.