Cyclic alphabet shift by a fixed step – find the next letter: U, B, I, P, W, ?

Introduction / Context:
This is a single-rule cyclic alphabet progression. Each term is obtained from the previous one by adding a fixed step size with wrap-around at Z. Detecting that constant step gives the immediate next letter.

Given Data / Assumptions:

• Sequence: U, B, I, P, W, ?
• Alphabet positions: A=1, …, Z=26 with modular wrap.

Concept / Approach:
Compute forward steps between consecutive letters using modular arithmetic. If the step remains constant, apply it once more to the last letter to get the answer.

Step-by-Step Solution:
U(21) → B(2): forward step = +7 (since 21 + 7 = 28 → 2 after wrapping by 26).B(2) → I(9): +7.I(9) → P(16): +7.P(16) → W(23): +7.Therefore apply +7 again: W(23) + 7 = 30 → 4 = D.

Verification / Alternative check:
Every gap is consistently +7 modulo 26. The pattern is linear and unambiguous, so the next letter must be D.

Why Other Options Are Wrong:

• F (+11), Q (+? from W), Z (+3), E (+? from W) all deviate from the fixed +7 rule.

Common Pitfalls:

• Treating the steps as absolute without wrap-around, which makes U→B seem inconsistent; modular counting resolves it.

Final Answer:
D