how often..
how often意为“多久……次、是否经常”,用来提问在某一特定的时间进行某个动作的次数,答语通常是always,usually,often,sometimes,once/twice a day/month等.
—How often do you get to school very early?你多久早到校一次?
—Usually.通常.
—How often do you see a film?你多久看一次电影?
—Once a month.每月一次.