如图，在△ABC中，∠C=90°，点D是BC边上一动点，过点B作BE⊥AD交AD的延长线于E．若AC=6，BC=8，则$\frac{DE}{AD}$的最大值为（　　）

铅笔盒放在水平桌面上静止时，在下列各对力中属于相互作用力的是

下列关于哺乳动物运动系统的叙述，不正确的是（    ）

    I am John. I always get up late at the weekend. At about 9:30 am, I have breakfast. After breakfast, I start doing my homework. We have lunch at about 12:00, and then I watch TV or have a rest. I like reading and I often read some interesting books in the afternoon. I like sports, too. Sometimes I play football or basketball with my friends at school. My school is near my home, so I can walk there. Every weekend, my father takes me to a restaurant for a big dinner. I can enjoy lots of nice food. I like my weekend.