用于测定硝酸盐氮的水样,在加浓盐酸至pH值为1~2的条件下,样品可保存()时间。
A、3d
B、5d
C、10d
D、7d
参考答案:D
It is said _______ ________ was all ________ he said. [ ]
A. that; that; that
B. what; what; what
C. that; which; what
D. that; that; what
铜片在空气中加热时,可观察到_______,该反应的文字表达式表示为_______。