What are the three steps a driver should take before backing a large vehicle?

Answer: B — Look at the backing area, check clearances, and observe mirrors while backing slowly

Before backing a large vehicle, drivers should first look at the backing area to ensure it is clear of any obstacles or pedestrians. They should then check the clearances around the vehicle, such as trees, signposts, and other vehicles. While backing, drivers should also be observing their mirrors constantly to ensure they have enough space and are not at risk of hitting anything. Option A is incorrect because backing quickly and sounding the horn are not safe practices and may cause accidents. Option C is incorrect because adjusting the mirrors and starting the engine are not enough preparation before backing a large vehicle. Option D is incorrect because calling for a guide and stopping frequently are not necessary if the driver has properly checked the backing area and is moving at an appropriate speed. These options may also cause distractions and increase the risk of accidents.