The correct answer is A. Methanol.
Methanol is a type of alcohol that can be mixed with diesel fuel to reduce carbon monoxide emissions. When methanol is mixed with diesel fuel, it helps to improve the combustion process and reduce the amount of unburned fuel that is released into the atmosphere. This can lead to a significant reduction in carbon monoxide emissions.
Alcohol is a general term for a group of organic compounds that contain one or more hydroxyl groups (-OH). Alcohols are found in many different forms, including ethanol, methanol, and isopropanol. Ethanol is the type of alcohol that is found in alcoholic beverages. Methanol is a toxic alcohol that can be fatal if ingested. Isopropanol is a less toxic alcohol that is often used as a solvent.
Phenol is a type of alcohol that is found in coal tar and petroleum products. Phenol is a toxic substance that can cause skin irritation, respiratory problems, and cancer.
In conclusion, methanol is the only option that can be mixed with diesel fuel to reduce carbon monoxide emissions. Alcohol, ethanol, and phenol are not effective at reducing carbon monoxide emissions.