often是频率副词,和sometimes,always,never,frequently等一样表示习惯性.
后接动词原形用于一般现在时.
后接动词过去式用于一般过去时.
例如：I often go to the library on Sundays.我经常星期天去图书馆.
I sometimes went the park on weekends.我过去有时候周末去公园.