Final answer:
The percentage of China's total energy supply that comes from burning coal is approximately 60%, making 60% the correct answer.
Step-by-step explanation:
The question pertains to the percentage of China's total energy supply that comes from burning coal. Based on the provided information, the closest approximation we have is that coal account for close to 2/3 of China's energy mix, which would be approximately 60%. Given the options: a) 25%, b) 40%, c) 60%, and d) 75%, the correct answer to the student's question is c) 60%.