Answer:
Walk or use a bicycle for short distance travel - reducing CO2 emissions that contribute to climate change
Use computers for communication and taking notes - saving forests
Treat sewage water and use it in factories - conserving freshwater aquifers
Step-by-step explanation:
Walking or using a bicycle for short distance travel, as opposed to using cars, helps reduce CO2 emissions because neither humans nor bikes emit as much CO2 as cars. Alternatively, carpooling or using public transportation also helps reduce CO2 emissions.
Using computers as opposed to paper for communication and taking notes reduces the amount of paper that is produced (theoretically according to the law of supply and demand), thereby saving forests.
Treating sewage water and using it in factories ensures that this dirty water is not released into the environment. Sewage water released into local waterways often has catastrophic effects for local flora and fauna, who are not used to living in the presence of toxic chemicals.