A:维修用电器时一定要切断电源
B:有金属外壳的用电器,金属外壳一定要接地
C:发现有人触电应先救人后断电
D:为了保证家庭电路安全,尽量不要同时使用多个大功率电器
秋千荡到最高点时,如果受到的力全部消失,下列现象可能会发生的是( )
读我国西气东输工程示意图(如下图),完成下列问题。
October the ____ was National Day. I went to Hawaii for vacation ____ my family. We went to the airport first and went to Hawaii by ____. We lived in a small hotel for a night. The next morning we went ____ in the sea for 2 hours, we ____ very happy. So we lay on the ____ to have a rest. Then we walked back to the hotel. On our ____ to the hotel, it began to ____. And we didn't have an umbrella with us. We all got____. ____ a bad vacation!
东东在实验时,①先用一块洁净的擦镜纸擦拭目镜,
②再进行对光处理,直至通过显微镜目镜看到一个明亮的圆形视野,
③然后将玻片标本放在显微镜载物台正中央,用压片夹夹住.
④接着转动粗准焦螺旋,眼睛从侧面看着物镜,使镜筒缓慢下降,将物镜下降至接近玻片标本.
⑤用左眼朝目镜里观察,同时转动细准焦螺旋,缓缓上升镜筒,直到看清物像为止.
在上述的描述中,东东的操作有错误的是( )