Fill the four gaps to complete the reverse-ordered cluster: Z Y X — W — Y Z Z — X W W X Y —

Introduction / Context:
The run displays a reverse-then-forward interleave over W, X, Y, Z. The gaps must admit the natural continuation “W X Y Z”.

Given Data / Assumptions:
Markers show ZYX followed by later XWWXY, suggesting the mid-segment is WXYZ.

Concept / Approach:
Insert the canonical quartet and verify no adjacency contradicts the local flow.

Step-by-Step Solution:

Verification / Alternative check:
Check each 3-letter window around gaps; all remain consistent.

Why Other Options Are Wrong:
They permute the quartet in ways that break at least one adjacency.

Common Pitfalls:
Overlooking that both upstream “ZYX” and downstream “XWWXY” constrain the middle strictly.

Final Answer:
WXYZ