介词是一种虚词,它不可以单独使用。它后面常跟上名词、代词等构成介词短语,在句中可作主语、宾语、补语或表语等成份。但由于句子结构的变化,介词有时可以单独位于句末。现将其用法归纳如下1.当介词的宾语是疑问词时,介词可置于句末。例: Prepositions are a kind of function word. It cannot be used alone. It is often followed by nouns, pronouns, etc. to form prepositional phrases, which can be used as subjects, objects, complements, or predicative elements in sentences. However, because of the change in sentence structure, prepositions can sometimes be located at the end of a sentence. The usage of the preposition is summarized as follows: 1. When the object of the preposition is an interrogative, the preposition can be placed at the end of the sentence. example: