题目

People think that writing short stories is easy because they are short. But in fact they are hard to write well. There are only a few writers of good short stories and the American writer O. Henry is one of them. His real name was William Sydney Porter and he grew up in North Carolina. He was not very successful at school but he loved reading. When he was about twenty years old he left North Carolina and moved to Texas. He thought there would be more opportunities for work there. At first he worked on a newspaper but as this did not provide enough money he changed his job. He decided to 如图，已知C是线段AB上的任意一点（端点除外），分别以AC、BC为斜边并且在AB的同一侧作等腰直角△ACD和△BCE，连结AE交CD于M，连结BD交CE于N，给出以下三个结论：①MN．．AB；②；③.其中正确结论的个数是（A）0         （B）1           （C）2             （D）3