Which statements show the importance of clean air? Check all that apply.

•Air is a natural resource.
•Governments manage air pollution to provide clean air.
•Lungs naturally purify the air, so air pollution does not harm people.
•Ultrafine particles contribute to 17,000 deaths per year in the United States. Particles in the air cause health problems.

Which experiment would most likely contain experimental bias

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area

Cells destroy body cells infected by a virus or bacteria. killer t t memory t none of the above