|A) Air pollution||B) Sound pollution|
|C) Noise pollution||D) Water pollution|
1. Lichens are plants that grow in exposed places such as rocks or tree bark.
2. Lichens are widely used as environmental indicators or bio-indicators. They can be used as air pollution indicators, especially of the concentration of sulfur-di-oxide in the atmosphere.
3. They need to be very good at absorbing water and nutrients to grow there.