题目

阅读下面短文，根据其内容写一篇60词左右的内容概要。 Tired of all the pushing in supermarkets?Fed up with waiting in endless lines to pay for what you have bought? Angry at wastingtime in traffic jams only to find no parking spaces when you eventually arrive atthe store? If this is you, then online shopping is the answer to your dreams oftrouble-free shopping, or is it? Online shopping brings its own challenges.Here are a few things to bear in mind when browsing (浏览) various websites. Theclaim (声明) made by online sites is that shopping onlineis a safe and sec下列计算中正确的是（　　）A．a3•a4=a12B．（a2）3=a5C．（x-y）2=x2-y2D．2x-3x=-x