一、介词介词是一种虚词,不能单独做句子成分,必须和名词或代词构成介词短语。注意以下常用介词的区别:1.at,in,on和by表示时间的区别:at表示:1)具体的时间点。例如:They came home at noon(at night,at ten o clock,at daybreak,at dawn).2)一般较短暂的一段时间,但在如Christ A prepositional preposition is an imaginary word, which cannot be used as a sentence component alone, and must consist of prepositional phrases with nouns or pronouns. Note the difference between the following common prepositions: 1. at, in, on, and by means the difference in time: at: 1) Specific time. For example: They came home at noon (at night, at ten o clock, at daybreak, at dawn). 2) Generally shorter period of time, but in such as Christ