Which of the following is part of the emission control system?

The EGR (Exhaust Gas Recirculation) valve is integral to the emission control system because it helps reduce nitrogen oxide (NOx) emissions produced during the combustion process in an engine. It works by recirculating a portion of the engine's exhaust back into the intake manifold, which lowers the combustion temperature and, consequently, reduces the amount of NOx produced. This process is crucial for meeting various environmental regulations aimed at controlling air pollution and improving air quality.

The other components listed do not play a direct role in emissions control. The fuel pump is responsible for supplying fuel to the engine, the starter motor is essential for cranking the engine to start it, and transmission fluid is related to the operation of the vehicle’s transmission and does not influence exhaust emissions. Therefore, the EGR valve is specifically designed for emission control and is key in helping vehicles comply with emission standards.