下列关于预防医学的提法中，错误的是（） A.它以人群为主要研究对象 B.它以环境-人

Dear David,
     Please    1    to my home for    2    at six this evening. Now let    3    tell you    4    to get to my home.
When you walk out of school, you should    5    a No.2 bus and then    6    at Xinhua Road. Then turn rigt
into Dongfeng Street and walk    7    this street. Take the first turnig    8    the left. My home is in the third
building on the right. There is a big tree    9    the building. I live on the fifth floor. And I'll   10   for you at
the gate. 
                                                                                                                                                Yours, 
                                                                                                                                                 Li Lei