副词只起到修饰作用，不影响句子的语法转换。所以，看动词依句子意思而变，与副词无关。如：I am seldom ill.我很少生病。It is seldom that a man lives to be a hundred years old.人生百岁古来稀。
知识拓展
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;非实义动词分为:1系动词be.2助动词，帮助动词构成时态(do,does,will,shall,have,had,has).3 情态动词(must,can,may)。除此之外，都叫做实义动词。
常见频度副词按频率大小排列如下:
always(100%)>usually(80%)>often(60%)>sometimes(40%)>seldom(20%)>hardlyever(10%)>rarely(1%)>never(0%)
频率副词用在be动词后。He is always late for class.他经常迟到。
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。
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。
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。
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?(误)Yes, I do often.是的,我常去。(正)Yes, I often do.
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。Never have I been there.我从未去过那里。Seldom do I watch TV.我很少看电视。
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。I go to school by bike usually.我通常骑车上学。
