Select the letter-cluster from among the given options that can replace the question mark (?) in the following series. QAZ, RBY, SCX, TDW, ?

Correct — B.
Rule: +1, +1, −1 — the first two letters step forward, the third steps back.

First letters: Q, R, S, T → U
Second letters: A, B, C, D → E
Third letters: Z, Y, X, W → V

U, E, V together give UEV → option (b).

Why the others are wrong

• (a)
  UBS — UBS gets the first letter right, but the second letters run A, B, C, D, so the next is E, not B. The third should be V, not S.
• (c)
  JKS — JKS breaks the first-letter run Q, R, S, T. One step on from T is U, and J does not continue that run.
• (d)
  VSA — VSA starts with V, two steps after T. The first letters move one step at a time, so the cluster must start with U.

Split each cluster into three separate series and read them column by column. The first letters climb Q, R, S, T and the second letters climb A, B, C, D, one step each. The third letters fall Z, Y, X, W, one step back each.

The second and third letters are also opposite pairs: A–Z, B–Y, C–X, D–W. Each pair's positions add to 27, so E pairs with V (5 + 22 = 27), a quick check on UEV.

Key facts

• Q = 17, R = 18, S = 19, T = 20, U = 21 in alphabet positions.
• Opposite letters add to 27: A–Z, B–Y, C–X, D–W, E–V.
• E = 5, J = 10, O = 15, T = 20, Y = 25 are quick reference points for counting positions.

Common traps

• Picking UBS because it starts with the right letter, without checking the second and third letters
• Assuming all three positions move forward, when the third letter runs backwards

No directly related past PYQ was found.