What is the required minimum speed limit on most highways?

Answer: D — 55 mph

Most highways have a minimum speed limit of 55 mph, which is the recommended speed to maintain traffic flow and reduce the risk of accidents. Option A, 25 mph, is too slow for highway driving and may cause congestion. Option B, 35 mph, is also too slow for highways and may lead to increased travel time and frustration for other drivers. Option C, 45 mph, is closer to the minimum speed limit but is still considered too slow for highways. Option D, 55 mph, is the appropriate speed limit for most highways and is the best option out of the given choices.