Each term is a three-letter block in strict reverse order; the block's first letter descends by 3 between terms.
- Blocks: QPO (Q→P→O), NML (N→M→L), KJI (K→J→I), ? , EDC (E→D→C).
- Start letters: Q → N → K → H → E (−3 each step).
Concept/ApproachIdentify the window size (3 letters) and the stride (−1 inside windows, −3 between windows).Step-by-Step calculation1) After KJI, subtract 3 from K ⇒ H; write H in reverse block: H, G, F ⇒ HGF.2) Next subtract 3 from H ⇒ E, yielding the given EDC.Verification/AlternativeSequence of start letters: Q(17), N(14), K(11), H(8), E(5) confirms −3 stride.Common pitfallsProposing ascending JKL (opposite to the within-block direction) or miscounting the start-letter stride.Final AnswerHGF
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