Answer the following question given this paragraph: 

All life relies on a relatively narrow range of pH, or acidity. That’s because protein structure and function are very sensitive to pH. Air pollution can cause precipitation to become acidic. Nitrogen and sulfur oxides, mainly from motor vehicle exhaust and coal burning, create acids when they combine with water in the air. The acids lower the pH of precipitation, forming acid rain . If acid rain falls on the ground, it may damage soil and soil organisms. If it falls on plants, it may kill them (see Figure below ). If it falls into lakes, it lowers the pH of the water and kills aquatic organisms.


Q: When the ph of precipitation is lowered because of air pollution, what results?

 Choices:

- abnormal rain

- climate change

- sleet

- acid rain

A:
acid rain
