介词的概念:表示它后面的名词或代词与其它句子成分的关系。1.介词种类:①简单介词:如in,on,at等;②介词短语:如in front of,instead of等。2.表示时间的介词(1)表示年、月、日、时刻等用:in,on,at;①at:用于表示时刻、时间的某一点。 The concept of preposition: the relationship between the noun or pronoun behind it and the composition of other sentences. 1. preposition types: ① simple prepositions: such as in, on, at, etc .; ② prepositional phrases: such as in the front of, instead of and so on. 2. Prepositions that represent time (1) that the year, month, day, time, etc. used: in, on, at; ① at: used to indicate a certain point in time and time.