Explanation:

Bioindicators are species that can be used to monitor the health of an environment or ecosystem. Lichens and mosses are particularly sensitive to air pollution, especially sulfur dioxide ($\text{SO}_2$). They absorb nutrients and pollutants directly from the atmosphere, and their absence or specific growth patterns can indicate the level of air quality. Option (C) is correct because lichens and mosses are widely recognized as excellent bioindicators for air pollution. Option (A) is incorrect; Ferns and Cycas are vascular plants and generally not used as primary indicators for air pollution in the same way lichens are. Option (B) is incorrect; While algae can indicate water pollution, and liverworts are sensitive to environmental changes, they are not as broadly recognized as air pollution indicators as lichens. Option (D) is incorrect; Neem trees are resilient and not typically used as pollution indicators, and *Eichhornia* (water hyacinth) is a water plant that can indicate nutrient-rich (polluted) water, but not air pollution.