What is the function of a carburetor's starter (choke) circuit during a cold engine start?

1. It temporarily restricts air flow or opens an auxiliary fuel passage to provide a rich air-fuel mixture, helping the cold engine ignite fuel.
2. It advances the ignition timing to create a stronger spark.
3. It bypasses the throttle cable to keep the engine speed at maximum RPM.
4. It pumps extra lubricating oil into the cylinder head to prevent dry starts.