— Yes. One of his famous sayings, "Learn the new ________ reviewing the old", is very helpful to us.
A:while
B:until
C:before
在氢硫酸溶液中加入少量下列物质:①O2;②Cl2;③SO2;④CuSO4.能使溶液pH值减小的是( )
到三角形三个顶点距离相等的是( )
鱼能在水中呼吸,它的呼吸器官是( )