Which of the following letter-clusters will replace the question mark (?) in the given series?

UV, OY, IB, EE, ?

The correct option is AH.

To find the missing letter-cluster in the series UV, OY, IB, EE, ?, let us analyze the pattern of the first and second letters of each cluster separately.

1. Pattern of the first letters:
The first letters of the clusters are: U, O, I, E, ...
If we look closely, these are the English vowels in reverse alphabetical order:
U → O → I → E → A
Therefore, the first letter of the missing cluster must be A.

2. Pattern of the second letters:
The second letters of the clusters are: V, Y, B, E, ...
Let us analyze their positions in the English alphabet (A = 1, B = 2, ..., Z = 26):
V = 22
Y = 25
B = 2 (or 26 + 2 = 28)
E = 5 (or 26 + 5 = 31)
Let's find the difference between consecutive positions:
V (22) to Y (25) ⇒ 22 + 3 = 25
Y (25) to B (28) ⇒ 25 + 3 = 28 (which is B)
B (2) to E (5) ⇒ 2 + 3 = 5 (which is E)
Following this +3 pattern, the next letter's position will be:
E (5) + 3 = 8
The 8th letter of the English alphabet is H.

Combining the first letter (A) and the second letter (H), the next letter-cluster in the series is AH.