According to the passage, the numerical value of the concentration level of a

Câu hỏi :

According to the passage, the numerical value of the concentration level of a substance is only useful if __________.


A. it is in a localized area


B. the other substances in the area are known

C. it can be calculated quickly

D. the natural level is also known

* Đáp án

D

* Hướng dẫn giải

Đáp án D

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