题目

Health reports believe that even a little exercise is rather better than ___ at all. A . no one B . none C . nothing D . anything 答案：B已知等腰△ABC中，AB＝BC，P在底边AC上的任一点，PE⊥AB于点E，PF⊥BC于点F，CD⊥AB于点D.求证：CD＝PE＋PF.