The word "these" in the second paragraph refers to      A. the compounds moved to the water or soil

The word "these" in the second paragraph refers to     

A. the compounds moved to the water or soil

B. the various chemical reactions.

C. the pollutants from the developing Earth   

D. the components in biogeochemical cycles.

Trả lời

Air pollution requires a very flexible definition that permits continuous change

Chọn D

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