如图，Rt△ABC中，AC⊥BC，CD⊥AB于D，AC=8，BC=6，求AD的长．
若﹣3x2my3与2x4yn是同类项，那么m﹣n=（ ）
Hello!My name is Bob. My classroom is not big but nice. There are 21 desks and 20 chairs. 墙上有一些画和一幅地图。Mrs Brown is our English teacher. She is from a big city.She is nice. Her husband Mr Brown is a teacher too, but he isn't in our school. Tom is my good friend. We like playing football on Saturday. Where is my football? It is under my desk.
一个钢瓶里装有压缩气体，当从钢瓶中放出部分气体后，瓶中剩余气体( )。
