A:K+、NO3﹣、SO42﹣、Cu2+
B:Ag+、K+、Cl﹣、NO3﹣
C:K+、NO3﹣、Na+、OH﹣
D:H+、Ba2+、Cl﹣、SO42﹣
一艘轮船每小时航行15千米,4小时可以到达目的地.如果要3小时到达,每小时应航行( )
A note was on the blackboard ______ “All those who have a fever must leave school right now”.
如图所示,在一水平长木板上放一木块P,缓慢抬起木板的右端,木块P和木板始终相对静止,则( )