_ are bioindicators of air pollution.

Explanation

Explanation:Correct answer is lichen as they are used as an bioindicator specifically for air pollution. Cyanobacteria are not typically used as bioindicators of air pollution, as they are more commonly found in aquatic environments such as lakes and oceans. Mycorrhizae are symbiotic associations between fungi and the roots of plants. While they can play a role in soil health, they are not typically used as bioindicators of air pollution. Fungi are important decomposers in the ecosystem, but they are not typically used as bioindicators of air pollution.