1. “三长”

(1) 介词短语

【定义】从介词开始到名词结束、表达一个独立的完整的含义的结构。

【起止标识】标记介词短语时，要从介词开始到介词之后的第一个名词终止。如：at home、in the school、in the beautiful park、during my happy childhood、over the last few years、for three weeks、to the destination

【例句】 (After chatting) (with Laura) (on this matter) (for two hours) (from 2:00 to 4:00) (in the afternoon), I returned (to my office).

(2) 从句

【定义】从句是复合句中不能独立成句，但具有主语部分和谓语部分，由that、who、whom、when、why、where、how、which、if、although等关系词引导的非主句部分。

【起止标识】标记从句时，一定从关系词开始，到以下四种终止。

① 到句尾终止，如：Li Hui is a teacher (who teaches English).

② 到句中的逗号终止，如：(When I was young), I listened to the radio.

③ 到下一个修饰成分终止，如：I will invite Yao Ming (who was a top basketball player) to Beijing. (to Beijing是介词短语，属于另一个修饰成分，故从句的标记在此处终止)

④ 到下一个谓语动词终止，如Yao Ming (who was a top basketball player) is studying in Shanghai.

(3) 非谓语动词短语

【定义】非谓语动词是指动词在句子中“不是谓语”时的几种变化形式，主要包括动词不定式、动名词和分词(现在分词和过去分词)三类。非谓语动词不能独立作谓语，而是充当句子的其他成分。由非谓语动词开头的、表示一个独立、完整的含义的结构叫做非谓语动词短语。

【起止标识】标记非谓语动词短语时，一定是从动词不定式(to do)、动名词(doing)或分词(现在分词doing或过去分词done)开头，到以下四种情况终止。

① 到句尾终止，如：Li Hui is a teacher (teaching English).

② 到句中的逗号终止，如：(To improve my English), I often listen to the English radio.

③ 到下一个修饰成分终止，如：Jack walked into the hall, (waving) to the audience. (to the audience是介词短语，属于另一修饰成分。)

④ 到下一个谓语动词终止，如：We, (singing a happy song), rode to school.