小萍想利用录音盒、一支滴管、清水及普通放大镜来制作一个显微镜，她组成了如图所示装置，请回答下列问题：

（1）对凸透镜有何要求？

（2）观察时要注意什么？

—Summer.

1. Please clean up before leaving.
2. Showers(淋浴)to be taken before 11 p.m..
3. No staying out after 10 p.m. unless allowed by me.
4. You may have incoming calls on my phone but no outgoing calls.
5. Bed time is 11 p.m.
6. Dinner is at 7 p.m. unless notified(通知). (If you don’t have dinner, you must let us know before 6 p.m.)
7. Keep noise to the least.
8. No smoking in the bedroom. 
The Address you are staying at is:   112 Kendal Way   Cambridge 
My contact number:    07870 347980

读我国某区域图，回答下列各题 。

A，B两站相距s，将其分成n段，汽车无初速由A站出发，分n段向B站作匀加速直线运动，第一段的加速度为a．当汽车到达每一等份的末端时，其加速度增加 $\frac{a}{n}$ ，求汽车到达B站时的速度．