You must sweep the floor.

问题描述:

You must sweep the floor.
为什么用THE,

the 是指特制那块地板,如果让你去干活,肯定是要给你划定区域了.
用a的话,意思就变成好像有多块地板,你随便搞干净一个就好,当然,即使是多选一,一般习惯也不这么说,会说,you must sweep one of these floors.