观察者根据自己的经验来判断被观察者心理正常还是异常属于下列哪一类标准化区分（）
A.医学标准
B.统计学标准
C.经验标准
D.社会适应标准
参考答案：C
The research mainly deals with the difficulty the students have ________ their attention on their
study all the time. [ ]
A. to focus
B. to be focused
C. focusing
D. focused
梅雨天气有何特点？出现在什么季节？哪些地区？
