year ago,时间状语
He graduated 2 years ago.
year before,before 可作连词和介词,后面可以跟句子或短语
Tom had worked for one year before his father retired.
有时before后也有省略用法
year ago,时间状语
He graduated 2 years ago.
year before,before 可作连词和介词,后面可以跟句子或短语
Tom had worked for one year before his father retired.
有时before后也有省略用法