A:电键闭合和断开的瞬间
B:电键闭合,移动滑动变阻器的滑动触头
C:电键闭合后线圈A在B中插入或拔出
D:只电键保持闭合
- Do you know Victory Day in China?
- Yes, it's _______ September 3rd _______ each year. It tells the world that Chinese people love peace and hate wars. Chinese people will never forget the history.
将同一实心铁球分别投入水、煤油和水银中,静止后铁球位置如图所示.已知ρ煤油<ρ水<ρ铁<ρ水银,则铁球受到的浮力最大的是( )
问卷调查有下列步骤,请按顺序排列为____ (填序号).
①发下问卷让被调查人填写;②设计问卷;③对问卷的数据收集整理;④收起问卷.