Which of the following letter-clusters can replace the question mark (?) in the given series to make it logically complete?
PQR, RTV, TWZ, VZD, ?

​​Given: PQR, RTV, TWZ, VZD, ?
Logic: first, second and third letter increased by 2, 3 and 4 respectively.
In first word to second word:
First letter P(16) + 2 = R (18),
Second letter = Q (17) + 3 = T (20),
Third letter R (18) + 4 = V (22)
Apply the logic:
For (?):

First letter = V + 2 = X,

second letter = Z + 3 = C,

third letter = D + 4 = H
Final Answer: (d) XCH ​​