A. the pollutants from the developing Earth
B. the components in biogeochemical cycles
C. the compounds moved to the water or soil
D. the various chemical reactions
B
Đáp án B
“these” được thay thế cho “the components in biogeochemical cycles” trong câu phía trước: “As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles.”
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