Select the letter-cluster that can replace the question mark (?) in the series…

To find the missing letter-cluster, we must determine the pattern of change for each letter position across the series: HTX, ?, FNT, EKR, DHP.

Step-by-Step Analysis
We will analyze the change for each of the three positions in the clusters:

First Letter Position:

H (8) → ? → F (6) → E (5) → D (4)

The pattern is a consistent decrease by 1.

Between H (8) and F (6), the letter must be G (7).

Second Letter Position:

T (20) → ? → N (14) → K (11) → H (8)

Let's check the differences:

N (14) to K (11) = -3

K (11) to H (8) = -3

The pattern here is a consistent decrease by 3.

Between T (20) and N (14), if we subtract 3: T (20) - 3 = Q (17).

Verifying: Q (17) - 3 = N (14). This works!

Third Letter Position:

X (24) → ? → T (20) → R (18) → P (16)

Let's check the differences:

T (20) to R (18) = -2

R (18) to P (16) = -2

The pattern here is a consistent decrease by 2.

Between X (24) and T (20), if we subtract 2: X (24) - 2 = V (22).

Verifying: V (22) - 2 = T (20). This works!