采煤机械化程度越高,产生的煤尘量()。
A.越大
B.越小
C.与采煤机械化程度无关
参考答案:A
操作显微镜时,完成下列哪个动作时眼睛一定要看着物镜?( )
A.对光
B.观察物像
C.上升镜筒
D.下降镜筒
________ can make people healthy.
A.Doing more exercise
B.Watching TV too much
C.Going to school without breakfast
D.Going to bed too late at night