直角三角形两直角边分别为5、12，则这个直角三角形斜边上的高为（  ）.

先通读下面的短文，掌握其大意，然后从A、B、C、D四个选项中选择可以填入空白处的最佳答案．

Dear Tony,

    I'm glad to1you．Now let me tell you something about my2life．I was born in3village．It was not big but4was beautiful and clean．There5a big garden．Near the garden was my first school，6I walked to school.My first teacher was7 and nice,but she was also8us.My best friends are Wang Mai and Li Dong.Wang Mai was good at all9and he was the top pupil(尖子学生)．Li Dong was good at football and he was a member of our school football team．

    I am looking forward to going back to my school and 10 my teachers and friends．

Yours，

Du Ming

战国时期人们根据磁石的特性制成“司南”，这是世界上最早的指南仪器。（   ）