I was on my way home with a friend yesterday ____ I found a mobile phone by the roadside. After picking it up, I suggested that we go to the house in front of which we found the mobile phone. And we did so. I ____ (knock) at the door and two young men answered. Neither of them had lost ____(they) phones, but as I referred to some names on the contact list(通讯录), one of them said he also had those ____(name) and that it must be the phone of one____their friends. Then, he took the phone and said how wonderful it was that I took the time____(find) the owner. Afterwards, I left without ____(leave) my name or address. I never considered keeping the phone. Instead, I immediately tried to find ____ owner. And I believed that was ____(exact) what I would want someone to do if I lost my phone. It couldn't have been ____ (good).

    Sometimes, helping others is just doing the right thing.

两千多年前，我国的学者墨子和他的学生做了小孔成像的实验．他的做法是，在一间黑暗的屋子里，一面墙上开一个小孔，小孔对面的墙上就会出现外面景物的倒像．小华在学习了小孔成像的原理后，利用如图装置来验证小孔成像的现象．已知一根点燃的蜡烛距小孔20cm，光屏在距小孔30cm处，小华测量了蜡烛的火焰高度为2cm，则光屏上火焰所成像的高度为____cm．