Don't tell me you are … enough to believe his lies.

Analyze the question: The sentence is "Don't tell me you are ____ enough to believe his lies." We need an adjective that describes someone who is easily fooled or too trusting.

Explain the concept: This is a vocabulary-in-context question. Look at the meaning of the whole sentence and check each option.

Check each option:

• A. credible: This means believable, and it describes a thing or person that can be believed (e.g., "a credible witness"). It does not describe someone who believes others. It does not fit.
• B. childish: This means immature or behaving like a child. It could loosely fit, but it usually describes silly or immature behavior, not gullibility, and "childish enough to believe" is not the natural expression.
• C. modest: This means humble or not boastful. It has no link to believing lies.
• D. naive: This means innocent, inexperienced, and too ready to trust. "Naive enough to believe his lies" fits perfectly and is a common collocation.

Answer: The sentence becomes: "Don't tell me you are naive enough to believe his lies.

Tip: In "complete the sentence" questions, ask what quality would make someone believe lies. Words like naive, gullible, and foolish fit that idea. Also remember that credible describes what is believed, not the person who believes it.