Where is it illegal to park?
Answer: C — Both of the above.
Both options A and B are places where it is illegal to park according to Tennessee traffic laws. Parking within 15 feet of a fire hydrant can block access for firefighters during emergencies. Parking within 50 feet of a railroad crossing is prohibited to ensure that there is enough space for vehicles to maneuver safely in the vicinity of railway tracks. Therefore, option C is the correct answer as it includes both of these illegal parking locations. Option D, "Prepare to yield to oncoming traffic," is not related to illegal parking spots and is not applicable to the question.