When must you yield right-of-way at an open intersection?

Answer: D — All of the above

At an open intersection, you must always yield right-of-way to any vehicle that is already in the intersection, approaching from the opposite direction while you plan to make a left turn, and when entering or crossing a state highway from a secondary road. All of these situations require you to wait for the other vehicle to pass before proceeding to avoid any potential collisions. Therefore, the correct answer is D, as all the other options are possible situations where you must yield right-of-way at an open intersection.