Select the option that represents the letters that, when placed from left to right in the blanks below, will complete the letter series. S _ Y A _ F I K M _ S U W

Correct — B. Lay the thirteen slots out and read the gap between each pair of neighbours.

Rule: +3, +3, +2, +2, repeating, wrapping past Z back to A.

Filled in, the line reads S V Y A C F I K M P S U W.

S→V +3, V→Y +3, Y→A +2, A→C +2.
C→F +3, F→I +3, I→K +2, K→M +2.
M→P +3, P→S +3, S→U +2, U→W +2.

So the three blanks take V, C and P → option (b).

Why the others are wrong

• (a)
  UCP — UCP opens with U. The first gap must be +3, and S + 3 is V — U is only two letters on.
• (c)
  VCQ — VCQ ends with Q. After K and M the block restarts at +3, so the letter after M is P, and P + 3 = S closes the line as printed.
• (d)
  VBP — VBP puts B in the second blank. Y → A is +2, so the next step is +2 as well, and A + 2 = C.

Not every alphabet series moves by one constant step. The steps here run in a repeating group of four — two long, then two short — and the group restarts until all thirteen slots are filled.

The way in is to compute gaps between the letters you are given, including gaps that jump a blank. Y to A, A to C and C to F are all visible without filling anything, and they already show the block.

Key facts

• The step block is +3, +3, +2, +2 and it repeats three times across the line.
• The completed series is S V Y A C F I K M P S U W.
• Y to A is a wrap past Z and counts as +2.

Common traps

• Assuming a constant gap because the first two visible steps are both +3.
• Treating Y to A as a break in the series instead of a wrap.
• Filling the blanks front to back without re-checking the run after each one.

No directly related past PYQ was found.