Fill the four missing letters so the series cc — ccbc — accbcc — c — b remains consistent over a,b,c.

Introduction / Context:
The series shows fixed chunks “cc”, “ccbc”, “accbcc” suggesting an interleaving of a and b around dominant c runs. We need a 4-letter fill to keep that fabric intact.

Given Data / Assumptions:
Alphabet restricted to a,b,c. Four blanks filled left-to-right by the chosen 4-letter sequence.

Concept / Approach:
We prefer a fill that alternates a and b around the c clusters while respecting all visible anchors.

Step-by-Step Solution:

Verification / Alternative check:
List every 3-letter window; all transitions are legal under the inferred alternation.

Why Other Options Are Wrong:
They create a clash at at least one anchor (e.g., consecutive identical letters where alternation is needed).

Common Pitfalls:
Attempting uniform abc cycling instead of anchor-constrained alternation.

Final Answer:
abac