前面用介词in，例如：
1、They looked as if they hadn't washed in days.他们看起来好像已经有好些天没洗澡了。
2、They have the capability to destroy the enemy in days rather than weeks.他们有能力在几天内，而不是几个星期内消灭敌人。
3、There was more money around in those days.那年头比现在富裕。
在年代前用in，季节前用in，月份前用in，年月前用in在日前用on，月目前用Oil，年月日前用on，节日前用on。
