1.名词(n.)： 表示人、事物、地点或抽象概念的名称。
2.副词(adv.)： 修饰动词、形容词或其他副词,说明时间、地点、程度等。如：now, very, here, often, quietly, slowly.
3.动词(v.)： 表示动作或状态。如：am, is,are,have,see .
4.形容词(adj..)：表示人或事物的性质或特征。
主要分类
1) 时间和频率副词:now,then,often,always,usually,early,today, late, next,last day,already(已经),generally(一般地),frequently（频繁）,seldom（很少地）,ever,never,yet,soon,too, immediately（立即）, finally,shortly（很快）, before, ago,sometimes, yesterday. once，twice
2) 地点副词:here, there, everywhere, anywhere,somewhere, in, out, inside, outside, above, below, down, back, forward（向前地）, home, upstairs(楼上地), downstairs, across, along, round , around, near, off, past, up, away, on.
3) 方式副词carefully(仔细地), properly(适当地), anxiously(焦虑地), suddenly, normally(正常地), fast, well, calmly(冷静地), politely(有礼貌地), proudly(自豪地), softly, warmly ,slowly
4) 程度副词:much,little, very,rather(相当),so,too,still, quite, perfectly(完美地), enough, extremely(非常), entirely(整个),almost, slightly(细小地), hardly.
5) 疑问副词:how, when, where, why.what.
6) 关系副词:when, where, why.等。
7) 连接副词:therefore(因此),moreover(此外),however,otherwise(另外的),then,when ,where,how,why等