You are presented with the quiz "What are the affects of burning fuel on human health?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "carbon monoxide is a gas produced by furnaces and other devices that burn fuel" and "carbon Monoxide Carbon monoxide is a health hazard". So, what's the best answer to the question?

Select from the following. 1. emissions 2. They aid lung health. 3. direct damage to the lungs 4. They are a hazard. 5. The affects are mildly healthy 6. The fuel burns clean. 7. Greenhouse gases 8. Global warming
Answer:
4.