Final answer:
An assumption that could be made when arguing for universal helmet laws is that a. all motorcycle riders prefer wearing helmets for safety.
Step-by-step explanation:
An assumption that could be made when arguing for universal helmet laws is, All motorcycle riders prefer wearing helmets for safety. This assumption implies that most if not all motorcycle riders recognize the importance of wearing helmets to protect themselves in the event of an accident. It assumes that universal helmet laws would be widely supported by the motorcycle-riding community. This assumption supports the argument for creating and enforcing helmet laws to ensure the safety of all riders.