一道英语语法题!高手请进啊啊啊1.________beforeweleavethedayaftertomorrow,weshouldhaveawonderfuldinnerparty.A.HadtheyarrivedB.WeretheytoarriveC.weretheyarrivingc.wouldtheyarrive我选了A,答案选B先

　　一道英语语法题!高手请进啊啊啊

　　1.________beforeweleavethedayaftertomorrow,weshouldhaveawonderfuldinnerparty.

　　A.HadtheyarrivedB.Weretheytoarrive

　　C.weretheyarrivingc.wouldtheyarrive我选了A,答案选B

　　先谢谢各位，我这题很不理解，是对将来的虚拟还是对什么的虚拟。可以解释得详细一点么？