Carbon dioxide is:

• A. Regulated by fuel economy standards.
• B. Regulated by emission standards.
• C. Not regulated.
• D. Regulated by safety standards.

Answer: (A)

CO2 emissions from vehicles are controlled mainly through fuel economy standards because these rules cap how much fuel a car can use per mile, and the amount of CO2 produced is directly tied to fuel burned. Improving fuel efficiency lowers CO2 per mile, so meeting these standards reduces greenhouse gas output. Emission standards, by contrast, target pollutants like NOx, CO, and particulates, not the total CO2 itself, and safety standards deal with crashworthiness and occupant protection. So the best fit is that carbon dioxide is regulated by fuel economy standards.