Answer:
A. putting smoke into air
Step-by-step explanation:
Can't be B. because they are harming the water from dangerous chemicals. Not C. because they are harming the atmosphere from dangerous chemicals. Not D. because phospate is used in fertilisers and if that gets in water it will cause algae bloom a sudden growth in algae which will block light from coming in the river or lake and so hydrophytes(aquatic plants) will die and fish will not get any oxygen so will also die. The algae bloom creates toxic stuff because of competition and will make the river of lake dangerous to be in. We are only left with A. so that is the answer.