I just took a test in school today. What question was I asked?

Question I was asked: The burning of fossil fuels has added pollutants that contain sulfur atoms to the air. These pollutants have contributed to which of the following?

I just took a test in school today. What question was I asked?

Question I was asked: Stretching is considered an important step before engaging in sports. In an investigation to see whether stretching before physical exertion reduces sports injuries, who would the control group most likely be?

I just took a test in school today. What question was I asked?

Question I was asked:
Which gas makes up the greatest percentage of Earth's atmosphere?