What should you do if you are approaching an uncontrolled intersection?

Answer: B — Slow down and yield the right-of-way to vehicles on the right.

Approaching an uncontrolled intersection means that there are no traffic signals or signs to guide drivers on who has the right-of-way. This can be dangerous, as drivers may assume they have the right-of-way and cause accidents. Option A is incorrect because maintaining speed can be dangerous if there are other vehicles present. Option C is also incorrect because waiting for vehicles on the left to clear the intersection can cause delays and is not a safe approach. Option D is incorrect because honking your horn is not the appropriate action to take when approaching an uncontrolled intersection. The best course of action is to slow down and yield the right-of-way to vehicles on the right, ensuring a safe and smooth flow of traffic.