纠结中，不知道上哪个单元·

回复 2# linyueqin

thank you very much

haohao xuexiyixia

钱不够了，去赚啦

这可学生要多说多练，open和turn on,close 和turn off有什么好办法区分啊

thank you very much!!!!

thank you very much!!!!

thank you very much

谢谢.不过有没有课件？