题目

A. write B. what C.tips D.look E.sharedEvery time you go online, you leave a trail(痕迹).This is just like a real footprint. It reveals where you’ve been, how long you’ve been there and 【1】 you’ve been doing there. The information can be accessed so it is advisable to be careful when you are online. Here are four 【2】 to take care of your digital footprint.Don’t forget to log off(退出) when you leave a website, especially if you are using a 【3】 computer. If you don’t, someone may pretend to be you.Don’t tell anyone your passwords and don’t 【4】 them down in an o1．若A={1，3，5，7}，B={2，4，6}，C={（x，y）|x∈A，y∈B}，列出C中的所有元素．