Which letter-cluster will replace the question mark (?) to complete the given series?
RFTL, ?, VNLH, XRHF, ZVDD

Let's find the constant pattern across the terms:
First letter: R → ? → V → X → Z

V(+2)→X(+2)→Z

So, R(+2)→T.

Second letter: F → ? → N → R → V

N(+4)→R(+4)→V

So, F(+4)→J.

Third letter: T → ? → L → H → F

L(−4)→H(−4)→F

So, T(−4)→P.

Fourth letter: L → ? → H → F → D

H(−2)→F(−2)→D

So, L(−2)→J.

Combining these gives TJPJ.