coal and natural gas natural gas and nuclear energy nuclear energy and hydropower hydropower and coal
I gave my students this multiple choice question: Most electricity in the United States is generated using coal, natural gas, nuclear energy, or hydropower. Which of these add carbon dioxide to the atmosphere?

Only one answer is correct among these 4 choices:
- coal and natural gas
- natural gas and nuclear energy
- nuclear energy and hydropower
- hydropower and coal

Could you tell me which one is correct?

coal and natural gas