how often的用法例句：
He was shocked at how often she used the F-word.
她常常使用粗俗的骂人话，这使他感到震惊。
How often do you give your phone number out?
你经常把自己的'电话告诉别人吗？
No matter how often they turn up, their welcome never wears out.
不管他们多久露面一次，都永远那么受欢迎。
I don't know how often I heard the same awful jokes
这种千篇一律的烂笑话我不知道听过多少回了。
How often does it need to be changed?
大概要多久换一次呢？