当手、脚或身体沾湿或站在潮湿的地板上时，切勿启动电源开关和触摸电气用具。
参考答案：对
一个空心的铜球，其质量为178g，体积为30cm3．
（1）判断该球是空心的还是实心的，写出相应的判断过程．
（2）求这个铜球的空心部分体积．
（3）小华同学在此球的空心部分注满某种液体后，总质量为314g，求所注的液体密度． ρ铜=8.9×103kg/m3．
After putting on a self-contained breathing apparatus, you open the air supply and hear a continuous ringing of a bell.What does this mean?（）.
A.The unit is working properly
B.The face mask is not sealed properly
C.The air bottle needs to be refilled
D.The air supply hose has a leak
