How often:是对频率的提问
例如：how often does he purchase
他多久采购一次?
how many times :就是对次数进行提问：
如：how many times did he purchase in this year?
今年他采购了几次?
How many times就次数提问
how often 就频率提问
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.
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