in年in月in季节,如“in 2020”在2020年,“in april”在四月,“in summer”在夏天;in早中晚在本周,如 “in the morning ”、'in the afternoon'、'in the evening'、'in this week';具体到日就用on,如“ we are going to travel on march 1st”;at加准确点与分,如“at five a'clock”.
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