Choose the five letters to complete the pattern of a’s and b’s. Series: _ _aba _ _ ba _ ab

Introduction / Context:
This string-completion task involves inserting five letters into a template built around mini-blocks like “aba” and “ba”. The correct option must maintain consistent alternation while preserving these blocks.

Given Data / Assumptions:

• Framework: _ _aba _ _ ba _ ab
• Five blanks; one five-letter option placed left-to-right must fit globally.

Concept / Approach:
Use the anchors “aba” and “ba” as guides. Valid solutions avoid triple letters and support a-b alternations surrounding the anchors.

Step-by-Step Solution:
Insert "abbab": a b aba b b ba b ab. Read-through shows intact anchors and regular alternation, with no contradictory triple merges.

Verification / Alternative check:
Testing other choices reveals collisions (e.g., “bbb”) or misalignment with the final “ab” close.

Why Other Options Are Wrong:
abbba / baabb / bbaba: Each forces either heavy repeats or spoils anchor integrity.

Common Pitfalls:
Checking only the first or last two blanks; the middle anchors are decisive for correctness.

Final Answer:
abbab