讲义：
用法一：how often 指每隔多久，主要用来对频度副词或状语(如：once a week, three times a month 等)提问。如
-How often do you go to see the films?你多久去看一次电影？
-I hardly ever go to see the films.我几乎从不看电影。
-How often does he help with housework?他多久帮忙做一次家务？
-Maybe four times a month.可能一个月四次。
用法二：常见频率副词
例：My sister never eats junk food.
我姐姐从不吃垃圾食品。
Ninety percent of the students always use the Internet.
90%的学生经常上网。
用法三：次数的表达方法
例：We go to school five times a week. 我们一周去学校五次。
The magazine comes out once a month. 这杂志一个月出版一次。
