月份、季节、年等大时间前都用in，具体日子前用on。
例如：
in 2020，in January，in spring，in the morning，on August 8,2020.
相关介绍
例句：
There has been some decrease in military spending this year.
今年的军费开支有所减少。
This species of bird is decreasing in numbers every year.
这种鸟的数量在逐年减少。
Their music has become very commercialized in recent years.
他们的音乐近几年非常商业化了。
The next Rugby World Cup will take place in three years' time.
下一届橄榄球世界杯赛将于三年后举行。.
