You must not pass if you are _______ of a hill or curve.

Answer: A — fifty yards

When driving near a hill or curve where visibility is limited, it is essential not to pass other vehicles. This is because passing in such situations can be very dangerous, as you may not see oncoming vehicles until it is too late. By choosing Option A ("fifty yards"), you are ensuring that you maintain a safe distance near hills or curves, allowing you to react to any potential hazards effectively. It is crucial to prioritize safety on the road to avoid accidents and ensure the well-being of yourself and others.