What should you do when entering the motorway?

Answer: B — Give way to traffic already on the motorway

When entering the motorway, it is important to give way to traffic already on the motorway. This means that you need to check for a safe gap in traffic and gradually accelerate to match the speed of the other vehicles. Option A is incorrect because accelerating immediately to the speed limit could be dangerous if there is heavy traffic on the motorway. Option C is incorrect because the emergency lane should only be used in case of emergencies, not for merging onto the motorway. Option D is incorrect because sounding your horn is not necessary or recommended when merging onto the motorway. It may startle or irritate other drivers and could potentially cause a dangerous situation.