(C) Hind-Brain — Cerebellum
Walking in a straight line and riding a bicycle are possible due to the cerebellum, located in the hind-brain, which controls precision of voluntary actions and maintains posture and balance.
The passage explicitly states: "activities like walking in a straight line, riding a bicycle… are possible due to a part of the hind-brain called the cerebellum." Students often confuse cerebellum with cerebrum (fore-brain) or mid-brain — note that cerebellum is in the hind-brain, not the mid-brain. Option (B) is a common wrong answer because of this mix-up.
Source: Chapter 6, Section 6.1.2 Human Brain