问题补充：
—Will you join us in the party this Saturday evening?
—If I ,I would ;but I will have left for Japan on business by then.
A. am free
B. were to be free
C. will be free
D. would be free
答案：
A. am free
(答案→)B. were to be free
C. will be free
D. would be free
解析：考查虚拟语气：句意：--你将要参加周六晚上的派对吗？---如果我有空，我会的。但在那之前我将要前往日本经商了。but I will have left for Japan on business by then.可知有空的虚拟的，和将来相反的虚拟语气条件句用一般过去式或were to do，选B。
