ANS:A - mix air-fuel in the desired ratio.

The carburetor in a spark ignition engine is used to mix air-fuel in the desired ratio. The carburetor is a device that is responsible for combining air and fuel in the correct proportion for combustion in the engine cylinders. It atomizes the fuel and mixes it with the incoming air to create a combustible air-fuel mixture. This mixture is then fed into the engine cylinders for combustion. By adjusting various components within the carburetor, such as the throttle valve and the fuel jets, the air-fuel ratio can be controlled to meet the specific requirements of the engine under different operating conditions. This ensures efficient combustion and optimal engine performance. Therefore, the primary function of the carburetor is to mix air and fuel in the desired ratio before it is delivered to the engine cylinders for combustion.