Final answer:
The basal ganglia are primarily responsible for initiating movements, as well as regulating posture and motivation, with damage to these structures leading to motor impairments.
Step-by-step explanation:
The primary role of the basal ganglia in movement control is initiating movements (a). These interconnected brain areas assess cortical movement commands and compare them with the general state of the individual through modulatory activity. They facilitate the start and smooth execution of movements and are related to motor functions, as observed in conditions such as Parkinson's and Huntington's diseases. Damage to the basal ganglia results in motor impairments and can affect motivation and the regulation of posture as well.