How is a manual choke actuated?

A manual choke is designed to adjust the air-fuel mixture entering the engine for optimal combustion during cold starts. The correct answer highlights that the choke is operated directly by the user through a lever connected to the carburetor. This allows the operator to manually restrict airflow in the carburetor to create a richer fuel mixture, which is essential for starting a cold engine.

In contrast, the other options describe different methods of choke operation. Automatic operation based on engine temperature typically refers to an automatic choke system, which adjusts the mix without operator input. Electronic sensors represent a modern approach to engine management, with computer control rather than manual adjustment. A vacuum mechanism can be involved in some automatic choke designs but does not apply to the manual choke's operation, which relies solely on manual input from the user.