beforeyesterday是什么時(shí)態(tài)的標(biāo)志

　　The day before yesterday, she aired the room.

　　前天，她給房間通風(fēng)了。

　　His grandfather died the day before yesterday.

　　他的祖父前天去世了。

　　The accident happened the day before yesterday.

　　事故發(fā)生在前天。