Which of these protects the Earth from harmful radiation when found in the stratosphere, but is a pollutant at lower altitudes? A. carbon B. oxygen C. ozone D. hydrogen

The answer is the option c. fact. Indeed facts are the events such as they occur, without interpretations or opinions. Facts happens and they can be observed by different means: you can get them through sense organs (eye, ear, mouth, skin, nose) or with instruments. When you report facts you must clearly state them appart of your interpretation or opinion.