Answer:
D. "always" cover the microscope when not in use.
Explanation:
when you are finished using a light microscope or any microscope in general you always need to put the cover back on it. Mostly, to protect it from any harmful bacteria, light etc. and to keep it clean and, from collecting dust.
Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen, phosphorus, or both.
Eutrophication can be a natural process in lakes, occurring as they age through geological time.
Eutrophication was recognized as a pollution problem in European and North American lakes and reservoirs in the mid-20th century.
Human activities can accelerate the rate at which nutrients enter ecosystems.
It depends where is located or how is the health of a person, animal or thing
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