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

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

Phương pháp giải:

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