The doctor advised him to abstain ........................ smoking.

Correct option is C

"Abstain from" is the correct collocation. The preposition "from" is used to indicate avoidance or restraint from engaging in a particular action, such as smoking.
Information Booster:
1. "Abstain from" is a standard English phrase.
2. Indicates self-restraint or deliberate avoidance.
3. Commonly used in advice, formal writing, and health contexts.
4. Ensures clarity and idiomatic accuracy.
Additional Information:
· (a) of: Incorrect; doesn’t connect meaningfully with abstention.
· (b) in: Suggests inclusion, not avoidance.
· (d) about: Implies discussion, irrelevant here.