Insert one ordered 4-letter set to complete the pairwise pattern: ac_ga_eg_ce_.

Introduction / Context:
The string shows two-letter pairs separated by underscores: ac, ga, eg, ce, with four blanks. The task is to select one 4-letter sequence to fill these blanks in order so that all adjacent pairs exhibit a consistent cyclic relation.

Given Data / Assumptions:

• Visible pairs: a–c, g–a, e–g, c–e.
• Options to place in sequence: dbag, ecag, deag, ebdg.

Concept / Approach:
Observe that the right letter of one pair becomes the left letter of the next (…c → ga; a → eg; g → ce). This forms a cycle c → a → g → e → c. We therefore want the inserted letters to continue this cycle smoothly at each joint.

Step-by-Step Solution:
1) The cycle c→a→g→e suggests linking letters d and e as neutral bridges while preserving the “a-c-g-e” loop.2) Testing “deag”: placing d, e, a, g in the four blanks yields joints that keep the c–a–g–e turns intact and align the mid-sequence overlaps.3) Alternative candidates create mismatched turns (e.g., “dbag” pushes b into positions that disrupt the c→a or a→g transitions).

Verification / Alternative check:
Read the finished line and confirm that consecutive bigrams rotate through the cycle c–a–g–e without contradiction.

Why Other Options Are Wrong:

• dbag / ecag / ebdg: Each introduces at least one joint where the expected next pair is broken (e.g., c→b or a→c interruption).

Common Pitfalls:
Focusing only on individual pairs; you must track how each pair hands off to the next one.

Final Answer:
deag