how often后加过去时和一般现在时态中，不用于将来时；
how often
多长时间一次；
often
时常;常常;往往;大多
How often do you use the bus?
你多长时间坐一次公共汽车？
How often do you go to the theatre?
你多长时间看一次戏？
How often do you go swimming?
你多久去游泳一次？
How often do you exercise?
你多长时间锻炼一次？
水利万物而不争,
而万物莫能与之争。
