识读《三国鼎立形势图》，位于北方的 * * 是
A．西晋
B．魏
C．蜀
D．吴
答案：B
32.So often ______ in recent years that it has almost become a rule.
A．has this happened
B．this has happened
C．is this happening
D．for this to happen
课程内容存在的前提，也是培训课程开发的( )。
A．内在动力 B．外在动力 C．核心动力 D．开发动力
