The brain is responsible for

Option D is correct: the brain controls all three. Each function sits in a different region.

• Thinking belongs to the cerebrum, the largest part, which handles reasoning, memory, language and voluntary action.
• Heartbeat is regulated by the medulla oblongata in the brainstem. Its cardiovascular centre adjusts heart rate through the autonomic nervous system (sympathetic and vagus nerves). Option B is true, though it is a brainstem function, not a thinking function.
• Balance is coordinated by the cerebellum, which integrates inputs from the inner-ear vestibular system and proprioceptors to keep posture and movement steady.

Core concept: the brain is a set of specialised regions, not one undifferentiated organ. The split between voluntary and involuntary control is what matters here. A Mains link is brainstem death criteria in organ donation under the Transplantation of Human Organs Act, 1994, where loss of brainstem function is the key test.

Trap: aspirants pick A because thinking feels like the main function of the brain, and forget that involuntary life-sustaining functions are also brain-controlled. Read 'All of the above' carefully before eliminating options.