Air and water pollution are directly responsible for the loss of some species. in their studies of these pollution effects, biologists have determined that are especially sensitive to air pollution, and are now being used as an index of urban air quality.

Air and water pollution are directly responsible for the loss of some species. in their studies of these pollution effects, biologists have determined that lichens are especially sensitive to air pollution, and are now being used as an index of urban air quality.

The answer is texture

Carbon monoxide is the answer: )