跑道入口识别灯应该为每分钟60至()次的白色闪光灯,且闪光必须只能在向跑道进近的方向才能看到。
A、50
B、120
C、200
D、250
参考答案:B
指出下列实验操作造成的危害.
(1)倾倒试剂瓶里的药液时,标签没有想着手心______;
(2)实验剩余的药品放回原瓶______;
(3)向燃着的酒精灯里添加酒精______;
(4)加热液体时,试管口朝着有人的方向______;
(5)把容器放在桌子上使劲塞塞子______;
(6)滴管取用试剂后平放或倒置______.
Some people are born with the belief______ they are masters of their own while others feel____
they are at the mercy of others.[ ]
A. what;that
B. that;what
C. that;/
D. /;that