介词又称前置词,是英语中最活跃的词类之一,连接主语和表语,分简单介词和短语介词两种,简单介词及单个介词,如 in ,under ,on ,for ,after ,等,短语介词指多个单词构成的介词,如in front of ,out of ,instead of ,far from ,apart from 等.He is in the office.
情态动词本身有词义,但要与动词原形及其被动语态一起使用,表示说话人对有关行为或事物的态度和看法.情态动词后面加动词原形,如must,may,can,need,have to等等.you must go now.
助动词是语法功能词,自身没有词义,不可单独使用,如be,do,have等等,主要作用是构成时态和语态,例he is here.
副词用来修饰动词、形容词和全句,说明时间、地点、程度、方式等概念.如now,here,very,how,when,therefore等.Now he has gone,you may see him only when he comes back.
