单句改错。

1. You are supposed saying hello to your teacher in the morning.

                                                        ____________________.

2. I greet to my teacher politely every morning.

                                                                                               . 

3. I often drop at my English teacher's home on Sunday.

                                                                                               .

4. You are supposed not to make noise while eating noodles.

                                                                                              . 

5. What is the particular challenge that Jack is facing with now?

                                                      ____________________.

如图所示，A是一块水平放置得铅板的截面，其厚度为d。MM´和NN´是一重力可忽略不计，质量为m，带电量为q的粒子在匀强磁场中的运动轨迹。粒子的运动轨迹与磁场方向垂直，并且粒子垂直穿过铅板。轨迹MM´的半径为r，轨迹NN´的半径为R，且R > r。求：

（1）粒子穿过铅板时的运动方向（回答向上或向下）

（2）粒子带何电荷。

（3）粒子穿过铅板时所受的平均阻力。