For which of the following reasons can natural pollutants play an important

* Hướng dẫn giải

Đáp án B

Thông tin ở đoạn 2: “As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil.”