(C) Cerebellum
The cerebellum, a part of the hind-brain, is responsible for precision of voluntary actions and maintaining the posture and balance of the body.
Source: Human Brain, Chapter 6
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The passage clearly states: "a part of the hind-brain called the cerebellum… is responsible for precision of voluntary actions and maintaining the posture and balance of the body." Medulla controls involuntary actions like blood pressure; cerebrum (fore-brain) handles thinking; pons is not discussed in this context. Cerebellum is the only correct answer.