What is the maximum speed limit on highways if not otherwise posted?

Answer: D — 70 mph

Highways often have a maximum speed limit of 70 mph, unless otherwise posted. This is because highways are designed for higher speeds and typically have fewer hazards, such as intersections and pedestrian crossings, compared to other types of roads. Option A, 25 mph, is much too low for a highway and would significantly slow down traffic flow. Option B, 35 mph, is also lower than the typical speed limit for a highway. Option C, 65 mph, is a common speed limit for some highways, such as those with lower speed limits due to various factors, including weather or construction. However, 70 mph is the maximum speed limit for most highways in the United States, unless stated otherwise.