单选题
The author refers to lead and cadmium (line 18) in order to show
A、
(A) elements commonly used in biochemistry
B、
(B) elements that produce only a single desired product through their reaction
C、
(C) elements more common in nature than alkali metals
D、
(D) elements less efficient at producing electrical charges than alkali metals
E、
(E) elements which are sometimes used in simple reagent design
【正确答案】
E
【答案解析】
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