In which order are the emissions checks conducted?

The correct choice identifies the proper procedure for conducting emissions checks, which begins with high-speed testing, followed by low-speed testing. This sequence is significant for several reasons.

First, emissions systems are often designed to operate effectively across various speeds, but they can behave differently under different conditions. High-speed testing is important as it can reveal how well the vehicle's emissions system is functioning under load when the engine is operating at higher RPMs. It allows inspectors to observe emissions characteristics during conditions that more closely simulate real-world driving scenarios, where vehicles frequently operate at higher speeds.

Following with low-speed testing provides additional insights into the emissions performance of the vehicle in less stressful conditions. It allows inspectors to capture emissions data that might be indicative of issues that load or speed conditions can exacerbate, such as an improperly tuned engine or problems with the catalytic converter.

Thus, this ordered approach—starting with high speed and then moving to low speed—ensures a comprehensive understanding of a vehicle's emissions performance, leading to more accurate results in the inspection process.