What is the function of the carbon monoxide (CO) emission test for motorcycles in Sri Lanka?

1. To measure the concentration of unburnt fuel and carbon monoxide in the exhaust to ensure compliance with environmental regulations
2. To measure the amount of oxygen in the exhaust to check for air leaks in the muffler
3. To calculate the fuel efficiency of the carburetor at high RPM
4. To check if the engine oil is leaking into the combustion chamber