True or false: unlike four-wheel motor vehicles, under certain circumstances, insurance is not required to register motorcycles.

This is true. Four-wheel motor vehicles are always required to be registered, no matter what. However, there are certain circumstances in which two-wheel vehicles do not need to be registered. For example, motorcycles and motor-driven cycles (which are two different things) are required to be registered. However, mopeds and motorized scooters do not have to be registered, likely because these vehicles are unlikely to be on the road with other cars and motorcycles (which are much faster than mopeds and scooters).