现在完成时
现在完成时是用来表示过去发生的动作或状态对现在造成的影响。其句子结构为:主语 + have/has + 过去分词。其中,have用于第一人称(I, we)和第二人称(you)的主语,而has用于第三人称(he, she, it)的主语。
例如:
- I have finished my homework. (我已经完成了我的作业。)
- They have traveled to many countries. (他们已经去过很多国家。)
- She has not seen the movie yet. (她还没有看过那个电影。)
过去完成时
过去完成时是用来表示过去某个时间点之前已经完成的动作或状态。其句子结构为:主语 + had + 过去分词。
例如:
- By the time I arrived, they had already left. (当我到达时,他们已经离开了。)
- She had studied English for 5 years before she went to America. (她去美国之前已经学了5年英语。)
- They had not met each other before the party. (他们在聚会之前没有见过面。)