she has been to america twice

how often问的是“多经常”?,也就是动作发生的频率,多久一/两/三/n次
如：
How often do you go to see your parents?
Twice a week.
而
she has been to america twice
提问：twice两次,没有频率的意思,而是发生的次数,所以用how many times
How many times have you seen the movie?
Once一次
Twice两次
Three times.三次
Four times.四次

how many times 和 how often 有一点点区别 就是 how often 通常指现在经常或有频率的事情 而how many times 通常指过去了的 已经发生过的事情 多用于这里而已 其实区别就是这样 一般都不区分的 还有一点区别就是
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...