What is an appropriate action to take before downshifting while driving?

Answer: B — Before starting a hill

Downshifting before starting a hill is an important technique for maintaining control and optimizing performance when driving heavy vehicles. By downshifting before the incline, the driver ensures that the vehicle has adequate power and torque to ascend the hill effectively without stalling or losing momentum. This approach helps to keep the engine within its optimal power band, preventing it from overworking or straining. Moreover, downshifting in advance allows for a smoother transition and helps the driver maintain proper speed. If downshifting is delayed until after the vehicle is already struggling up the hill, it could result in a sudden loss of speed, making it more difficult to regain momentum and placing extra strain on the engine. This proactive strategy contributes significantly to road safety and vehicle longevity.