How can you use the engine to control your speed?

Answer: A — By changing to a lower gear

When using a vehicle with an engine, it is important to use the gears to control your speed. Changing to a lower gear physically lowers the gear ratio, requiring more effort from the engine to maintain the same speed. This can help slow down the vehicle, as opposed to accelerating quickly (choice B), which would increase your speed. Coasting (choice C), or driving without pressing on the accelerator, may slow your speed slightly, but is not an effective way to control your speed. Solely relying on brakes (choice D) can cause more wear on your brakes and may not effectively slow the vehicle down in certain situations. Therefore, changing to a lower gear (choice A) is the best option for using the engine to control your speed.