When entering an expressway from an entrance ramp, what should a motorist do before merging into traffic?

Answer: B — Check blind spots

Before merging into traffic from an entrance ramp, a motorist should check their blind spots to make sure there are no other vehicles in the lane they are merging into. This allows the motorist to safely merge without causing any accidents or disrupting the flow of traffic. It is important for motorists to be aware of their surroundings and check their blind spots before changing lanes or merging into traffic. Option A (changing lanes quickly) is incorrect because it is not safe to change lanes quickly without first checking for other vehicles. Option C (sounding the horn) is incorrect because honking the horn is not a necessary step in merging onto an expressway. Option D (accelerating) is incorrect because while a motorist needs to accelerate to match the speed of traffic, it should not be done without first checking for other vehicles and ensuring it is safe to merge.