一、介词in构成的短语表示时间1.表示某段时间内。常用在表世纪、季节、年份、月份和某一天的上午、下午、晚上。例如:in the1980s20世纪80年代in spring在春天in2009在2009年in May在五月in the evening在晚上2.表示在某段时间之后。例如:I will return in a few minutes/hours/days/months.我几分钟/几小时/几天/几个月后回来。二、介词on构成的短语 First, the preposition in the form of a phrase that time 1. That some period of time. Commonly used in the century, season, year, month and day of the morning, afternoon, evening. For example: in the1980s1980s in spring in spring in2009 in2009 in May in May in the evening at night2 indicates after a certain period of time. For example: I will return in a few minutes / hours / days / months. I’ll be back in minutes / hours / days / months. Second, the preposition on the phrase