Answer the following question given this paragraph: 

Poor air quality started to become a serious problem after the Industrial Revolution. The machines in factories burned coal. This released a lot of pollutants into the air. After 1900, motor vehicles became common. Cars and trucks burn gasoline, which adds greatly to air pollution.


Q: During what time period did poor air quality become a problem?

 Choices:

- Chernobyl disaster

- coal industry boom

- second world war

- industrial revolution

A:
industrial revolution
