Complete the binary-a/b pattern by inserting five letters so the full series is consistent. Series: _ a a _ b a _ b b _ a b _ a a b

Introduction / Context:
With only a and b present, we look for a staggered motif that keeps alternating neighborhoods consistent while honoring anchors.

Given Data / Assumptions:
Five blanks are filled left-to-right from a single 5-letter option.

Concept / Approach:
Prefer a fill that avoids forced double repeats next to anchors and preserves a balanced alternation density.

Step-by-Step Solution:

Verification / Alternative check:
Check each 3-letter window; all transitions are permissible.

Why Other Options Are Wrong:
They create unavoidable bb or aa collisions at an anchor that demand the opposite letter.

Common Pitfalls:
Not validating both early and late join points.

Final Answer:
bbaab