频率副词：一般用来表示动作发生的频率。往往放在句子中间，实义动词之前，非实义动词之后；
1.频率副词是表示与次数,频率有关的副词
如:always(总是), usually(通常),frequently（经常） often （经常）sometimes(有时), seldom(不常),rarely（很少），never（从不） once(一次), twice(两次)，等。
2.频率副词等级
almost , always 100%；
generally , usually 80%；
often , frequently 60-70%；
as often as not 40-50%；
sometimes , at times 20-30%；
occasionally , from time to time 10%；
hardly ever , seldom , rarely 5%；
never 0%。
3.频率副词用在be动词后
He is always late for class.他经常迟到。
4.频率副词用在主要动词前。
My father usually walks home.我的父亲经常步行回家。
5.频率副词用在助动词与实义动词之间。
I will always love you.我将永远爱你。
6.频率副词用在ought to之间。
You ought often to write to your mother.你应该常给你母亲写信。
7.在答句中,频率副词必须放在助动词前。
Do you often go there?你常去那里吗?-Yes, I often do.是的,我常去。
8.never(从不), seldom(很少,不常)用于句首时,句子要用倒装形式以加强语气。
Seldom do I watch TV.我很少看电视。
9.sometimes(有时）和usually（通常）可以放在句前和句末。
Sometimes I go to school by bus.我有时坐公交车上学。
