题目

— Could you please help me? We need another twenty chairs.    — Sure. I’ll do it right now.A.twenty chairs                  B.twenty more chairs  C.more than twenty chairs  D.as many as twenty chairs. 答案：B如图，已知△ABC中，AB=AC，BE平分∠ABC交AC于E，若∠A=90°，那么BC、BA、AE三者之间有何关系？并加以证明．