Normally a student would at least attend ______ classes each week.

单项选择题The student organizations seem to be effective in ______.

单项选择题According to the first paragraph an American student is allowed ______.

单项选择题Some students are enthusiastic for positions in student organizations probably because______.

单项选择题The erosion of the white cliffs in the south of England

单项选择题The experts study on the problem of erosion can______.