题目

Have you ever been sad because of failure? Please remember, for often.achieving what you set out to do is not the most important thing. A boy decided to dig a 36   hole behind his house. As he was 37   ,a couple of old boys stopped by to give a/an 38  . “What are you doing？” asked one of the 39  .“ I want to dig a hole all the way through the earth!” the boy 40  excitedly. The older boys began to 41  , telling him that digging a hole all the way through the earth was 42  . After a while, the boy picked up a jar(罐子). He 43  it to the visitors. It was full of all k7、在△ABC中，∠ACB=90°，CD⊥AB于D点，若BC=5，CD=3，则AD的长为（　　）A、2.25B、2.5C、2.75D、3