题目

阅读理解 阅读下面材料，根据材料内容和要求，从题后所给的四个选项中选择一个能回答所提问题的最佳答案。    There was once a guy who suffered from cancer, He was 18 years old and could die anytime.He stayed in his house and never went outside. He was sick of staying home and wanted to go outfor once. So he asked for his mother’s permission, who was his only lifelong friend.    He walked down his block and saw a CD store. He stopped and looked throgh the front door.He saw a beautiful gid about his age and knew it was love at first sight (看在△ABC中，AC=4，BC=3，∠ACB=90°，点D在AB上，且BD=2AD，求的值．