Motor vehicles that do not have ... are prohibited from being driven.

Correct answer

an exhaust silencer.

Regulations prohibit motor vehicles and mopeds that produce excessive noise from being driven, since this contributes to noise pollution and may be harmful to public health and the environment. This prohibition includes vehicles with incomplete, unsuitable or damaged silencers, or modified exhaust systems that do not meet legal requirements. Regulations also cover other aspects of vehicle emissions, prohibiting vehicles that emit smoke and gases in quantities exceeding the permitted limits. This includes vehicles that release unburnt fuel or emit smoke that may obstruct visibility and be harmful. Vehicles must be equipped with suitable devices to control these emissions and ensure that they operate within the established limits.