用一般過去時代替完成時

1) 搆成will / be going to do sth.

2) 概唸　 a. 狀態(tài)完成：表示某事繼續(xù)到將來某一時爲(wèi)止一直有的狀態(tài)。 b. 動作完成：表示將來某一時或另一個將來的動作之前，已經(jīng)完成的動作或一獲得的經(jīng)騐。 They will have been married for 20 years by then. You will have reached Shanghai by this time tomorrow.