This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Best Biological indicator of air pollution is 
Select and explain. 
A. Gambusia fish, B. Poecilia, C. Lichens, D. Algae
C: Lichens
Answer: C: Lichens 
Explanation: None