题目

如图，把一张矩形的纸ABCD沿对角线BD折叠，使点C落在点E处，BE与AD交于点F. ⑴求证：ΔABF≌ΔEDF； ⑵若将折叠的图形恢复原状，点F与BC边上的点M正好重合，连接DM，试判断四边形BMDF的形状，并说明理由. 答案：解： (1)证明：由题意得DE=DC=AB，∠A=∠E=90°， 又∵∠AFB=∠EFD，∴△ABF≌△EDF. (2)菱形. 证明：∵BE∥DM，AD∥BC，∴四边形BMDF是平行四边形. ∵△ABF≌△EDF，∴BF=DF. ∴四边形BMDF是菱形.阅读短文内容，从短文后的选项中选出能填入空白处的最佳选项，选项中有两项为多余选项。Many kids and teenagers have cell phones in their hands. However, is it really necessary for them to have phones at school? Here are the pros and cons.ProsThey can get in touch when necessary. The main benefit of having a phone is that your children can get in touch with you whenever they need to. 1. They can call the emergency services if necessary. If your children are in immediate danger, they can use their phones to call not only you but the emergency services. This is of great benefit and could potentially save your children’s lives. 2. As long as your children remember to do this , their phones won’t cause distraction(分心) in class. Giving them a standard instead of a smart-phone will also reduce the risk of distraction.ConsThe latest smart-phones can almost double as a computer. It means they offer far more of a distraction to kids than they used to. 3. All these characteristics could disturb your children’s concentration (注意力) if they play with them in class.Cellphones could interrupt lessons. Many children, even though they are asked to do so, forget to turn off their phones during lessons and their phones may make sounds. 4. Besides the distraction problem, cellphones can also be used to look up answers on the Internet. 5. The possibility of children having access to these during exams could be too attractive for them not to take advantage of.A. Cellphones can be turned off or put on mute.B. Children use ordinary phones instead of smart-phones.C. This allows you to feel they are safe and easy to reach.D. Without cellphones, campus life would be less colorful.E. They have some other functions — a calculator and the ability to save notes.F. This not only annoys other pupils, but also prevents them from learning well.G. Nowadays, children can not only text and make calls with their phones, but also play games, surf the Internet and listen to music.