Which entity provides guidelines that states must adhere to for emissions?

The correct answer is the Environmental Protection Agency (EPA) because it is the federal agency responsible for establishing and enforcing regulations pertaining to air quality and emissions. The EPA sets national standards for emissions, including those from vehicles, to ensure that the air quality meets health and environmental safety benchmarks. States are required to comply with these federal regulations and are given the authority to create their own programs to meet or exceed these guidelines.

The other entities listed do not have the same role in emissions regulation. The Department of Motor Vehicles primarily handles vehicle registration and driver licensing, but it does not set emissions standards. The National Highway Traffic Safety Administration focuses on vehicle safety standards and does not directly govern emissions. The Federal Bureau of Investigation deals with crime and law enforcement rather than environmental regulations. Thus, the EPA is the authoritative body that provides the guidelines that states must follow for managing emissions effectively.