day before yesterday的用法和样例：
例句
- If today is Friday, the day before yesterday is Wednesday.
假如今天是星期五，前天就是星期三。 - I see him the day before yesterday, but have not see him since.
前天我见过他，但后来再没见过他。 - If today is Wednesday, the day before yesterday was Monday.
今天要是星期三，前天就是星期一。 - I went shopping the day before yesterday.
我前天去购物了。
