Final answer:
The type of motor unit that can contract for many hours, or even days if necessary, is the large motor unit.
Step-by-step explanation:
The type of motor unit that can contract for many hours, or even days if necessary, is the large motor unit. A large motor unit is an arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle. These motor units are responsible for simple, gross movements and can sustain contraction for extended periods of time.