A:①②③
B:①③④
C:②③④
D:①②④
下列关于正比例函数y=﹣5x的说法中,正确的是( )
很多实验必须先制作装片,然后在显微镜下观察.下面的实验步骤错误的是( )
This chemical class is about the ______ of metals with oxygen and our teacher shows us how iron ______ air and water.