Fill the two blanks (in order) to complete the series: a b _ c b a _ b c c _ a a b c c b _ _ b c c b a

Introduction / Context:
Here the alphabet is restricted to a,b,c and the fixed letters suggest a sliding motif. We must pick a 5-letter insert that fits both blanks in order.

Given Data / Assumptions:
Two blanks are present, but the option provides a 5-letter sequence to be threaded through both blanks consecutively.

Concept / Approach:
Test each option and verify that local triplets keep the same rotation without contradicting any fixed letter at the join points.

Step-by-Step Solution:

Verification / Alternative check:
Check all join neighborhoods; no illegal transition occurs.

Why Other Options Are Wrong:
They force at least one clash (e.g., b next to b where the rotation calls for c).

Common Pitfalls:
Not threading the 5 letters strictly left-to-right across both blanks.

Final Answer:
abcab