机械设备的磨损可分为哪几个阶段（）
A.前期磨损
B.磨合磨损
C.后期磨损
D.正常工作磨损
E.事故性磨损
参考答案：B, D, E
如图所示是医生检查患者牙齿的情景，在金属 * * 面镜放入口腔前，先要将它放在酒精灯上烤一烤，以免水蒸气在镜面上 形成水雾。
What is an advantage of using foam in fire fighting?（）
A.It is MOST effective on very hot oil fires where the temperatures of the liquid exceed 100°C (212°F)
B.Most foams can be used with dry chemicals to attack a fire by two methods
C.Foam is effective on combustible metal fires
D.Foam can be made with seawater or fresh water
