A: Is that my mobile phone ringing? B: Leave it. You ... talk on your mobile phone while you're driving.

Choose the correct option.

The sentence implies a prohibition or a strong recommendation against talking on the mobile phone while driving, for safety reasons.

• have to: indicates obligation.
• mustn't: indicates prohibition.
• should: indicates advice or recommendation.
• can: indicates ability or possibility.

The context "Leave it. You ... talk on your mobile phone while you're driving." suggests that it is not allowed or is strongly advised against. Therefore, prohibition is the most appropriate meaning.

The correct option is 'mustn't'.