图中，任意相邻的三个小方块内的三个数的和是20．“？“代表的数是（　　）

请阅读Tony从美国发来的电子邮件，以李华的名义写一篇80词左右的回复。文中不得出现真实的人名、校名与地名。

Hey Li Hua

How are you? I've been busy since I came back from China. Guess what! I'm learning Chinese very hard, but I find it really difficult to learn Chinese well. Please tell me the best way you think.

One more thing, I hear you have Mid-Autumn Festival in China. What's the date of the festival? How do you celebrate?

Tony

探究凸透镜成像规律的现象和数据如表：（单位：cm）