When going down a steep hill, you should:

Shifting to a lower gear when going down a steep hill is a vital technique for maintaining control of the vehicle and ensuring safety. By utilizing a lower gear, the engine can help slow the vehicle down through engine braking, which reduces reliance on the brakes. This is particularly important when descending steep inclines, as it prevents brake overheating, which can lead to brake failure. The lower gear allows for better control of the vehicle's speed and stability, reducing the risk of skidding or losing traction.

The other options do not provide the same level of control or safety: accelerating can lead to an out-of-control situation, using cruise control can be dangerous on steep descents as it doesn't adapt to the changes in terrain, and maintaining the current gear may not utilise the benefits of engine braking effectively, especially on steep slopes where speed can rapidly increase.