Insert one ordered 5-letter string to complete the pattern: _c_ca_ab_bc_.

Introduction / Context:
The skeleton shows overlapping bigrams “c_”, “_c”, “ca”, “ab”, “bc” from the alphabet subset {a, b, c}. We must pick a 5-letter fill that restores the intended repeating chain.

Given Data / Assumptions:

• Skeleton: _ c _ c a _ a b _ b c _ (5 blanks)
• Options: abcac, babca, ccabb, acbba.

Concept / Approach:
We expect a cyclic run “…a→b→c→a→b→c…”. The best fill should yield recognizable overlaps like “ab”, “bc”, and “ca” at the designated joints without stutters.

Step-by-Step Solution:
1) Insert “a b c a c” in order.2) Early blanks form “…a c c a…”, aligning into “…a c | c a…”, then “…a b…”, then “…b c…”, producing the target overlaps.3) Other options either double consonants at bad spots (“ccabb”), invert transitions (“acbba”), or misalign the mid “ab→bc” hinge (“babca”).

Verification / Alternative check:
Scanning with bigram windows shows “ca”, “ab”, and “bc” occurring in the right places.

Why Other Options Are Wrong:

• babca: Misplaces the early transition and collides with the “c_” start.
• ccabb: Over-concentrates c’s and breaks the ab/bc alternation.
• acbba: Creates “bb” mid-sequence, which the skeleton does not support.

Common Pitfalls:
Not tracking how each blank affects the adjacent bigrams on both sides.

Final Answer:
abcac