Step 1: Understanding the Concept:
This question asks for a synonym for 'insinuate', which means to imply something indirectly.
Step 2: Detailed Explanation:
(A) Express: To communicate thoughts or feelings directly.
(B) Affirm: To state something as a fact confidently.
(C) Allude: To suggest or call attention to something indirectly, which is the definition of insinuate.
(D) Propagate: To spread an idea or theory widely.
Since 'insinuate' implies a subtle, indirect suggestion, 'allude' is the most accurate synonym provided.
Step 3: Final Answer:
The correct answer is (C) Allude.