Select the letter-cluster from among the given options that can replace the question mark (?) in the following series: RBEH, RGOW, RLYL, RQIA, ?

Correct — A.
Rule: R stays fixed, and positions 2, 3, 4 move +5, +10, +15.

Second: B, G, L, Q → Q(17) + 5 = V(22).
Third: E, O, Y, I → I(9) + 10 = S(19).
Fourth: H, W, L, A → A(1) + 15 = P(16).

That gives RVSP → option (a).

Why the others are wrong

• (b)
  RVSH — RVSH gets R, V and S right but ends in H. The fourth letters move +15: A(1) + 15 = P(16), while H is only A + 7.
• (c)
  RVHS — RVHS puts H third and S fourth. The third letters move +10 from I to S, and the fourth move +15 from A to P, so neither slot fits.
• (d)
  RSVP — RSVP holds the right four letters in the wrong order. The second letters move +5 from Q, which gives V, so S cannot come second.

A four-letter cluster with a fixed first letter is three series in one. Leave the fixed letter alone and read positions two, three and four down the terms.

Here the steps grow with the position: +5, +10, +15. The third and fourth positions pass Z inside the given terms, Y + 10 = 35 and W + 15 = 38.

Subtract 26 whenever a total passes 26: 35 → I(9), 38 → L(12), and L + 15 = 27 → A(1).

Key facts

• Q = 17, I = 9 and A = 1 become V = 22, S = 19 and P = 16.
• A total above 26 wraps: subtract 26, so 35 is I and 27 is A.
• RSVP and RVSP hold the same four letters, so the order inside the cluster decides.

Common traps

• Picking RSVP, the familiar abbreviation, which holds the right letters in the wrong order
• Stopping at 35 or 38 instead of subtracting 26, and deciding the rule has failed

No directly related past PYQ was found.