如图，把一张长方形纸片ABCD沿对角线BD折叠，使C点落在E处，BE与AD相交于点F，下列结论：

①BD=AD²+AB²；②△ABF≌△EDF；③ ；④AD=BD cos45°．其中正确的一组是（　　）

请写出实验步骤，画出实验数据记录表格．

    We are all learning English, but how can we learn English well? A student can know a lot about English, but maybe(可能) he can't speak English. If you want to know how to (如何) swim, you must get into the river. And if you want to be a football player, you must play football.
So, you see. You can learn English only by(通过) using(使用)it. You must listen to your teacher in class. You must read your lessons every day. You must speak English to your classmates and also you must write something sometimes. Then one day, you may find your English very good.