Final answer:
The cerebellum is the part of the CNS that is responsible for controlling coordinated movement, balance, and posture, making it the correct answer to the question.
Step-by-step explanation:
The part of the central nervous system (CNS) that controls coordinated movement, balance, and posture is the cerebellum. The cerebellum, often referred to as the "little brain," is located just below the cerebrum and behind the brain stem. It plays a crucial role in coordinating body movements and is also involved in movements that are learned through repeated practice. For example, activities like hitting a softball with a bat or touch typing on a keyboard heavily rely on the cerebellum. It contains many nerve pathways that connect with motor neurons all over the body to facilitate fine motor coordination. In contrast, the brainstem connects the brain with the spinal cord and controls several vital involuntary functions such as breathing and heart rate, but it does not primarily coordinate movement and balance.