What must a driver do before changing lanes?

Answer: A — urn on the vehicle's turn signals

Before changing lanes, a driver must turn on the vehicle's turn signals. This indicates to other drivers a change in position on the road and allows them to be aware of the driver's intentions. Checking the rearview mirror and honking the horn are not necessary steps before changing lanes. Increasing speed may actually be dangerous and is not a recommended action before changing lanes.