不定式通常由不定式符号to+动词原形构成,比如动词read的不定式便是toread。动词不定式具有名词、形容词及副词的性质,因此不定式结构在句中可作主语、表语、宾语、补语、定语等多种句子成分。一、不定式作主语。不定式可以在句中充当主语。例如:To meet you is a great pleasure.非常高兴见到你。To plant trees every year is necessary.每年植树是必要的。这种结构通常是在主语位置放个it作为形式主语,而把 Infinitives usually consist of infinitive symbols to + verb prototypes, such as the infinitive of the verb read, which is toread. The infinitive verbs have the properties of nouns, adjectives and adverbs. Therefore, the infinitive structure can be used as the subject, the idiom, the object, the complement, the attributive and other sentence elements in the sentence. First, the infinitive as the subject. Infinitives can be the subject of the sentence. For example: To meet you is a great pleasure. Nice to meet you. To plant trees every year is necessary. This structure is usually placed in the subject position it as a formal subject, and put