句型转换。

1. There are five boats in the river. (对划线部分提问)

______________ ______________ boats ______________ ______________ in the river?

2. It's three thirty now. (对划线部分提问)

 ______________ ______________ ______________ now?

3. This is a bus. (改为复数句子)

______________ are ______________.

4. Jenny walks to school. (改为一般过去时)

_________________________________________________________________________________

5. Jenny goes shopping with her mother. (改为一般将来时加tomorrow)

_________________________________________________________________________________

半径为a的圆环电阻不计，放置在垂直于纸面向里，磁感应强度为B的匀强磁场中，环内有一导体棒电阻为r，可以绕环匀速转动，将电阻R、开关S连接在环和棒的O端，将电容器极板水平放置，并联在R和开关S两端，如图所示．

（1）开关S断开，极板间有一电荷量为q、质量为m的带正电粒子恰好静止，试判断OM的转动方向和角速度的大小．

（2）当S闭合时，该带电粒子以