2.用法 (1)表示在将来某一时间之前已完成的动作,并可能对将来产生影响。 We shall have learned 12 units by the end of this term. 到这个学期末,我们将学完12个单元。 By the time you get home,I will have cleaned the house from top to bottom. 你到家之前我将已经把房子彻底打扫一遍了。