If you can't finish the work before Friday ,you may ________work on the weekend .选项有4个：A:must B:have C: have got to D:haven't to为什么是选B啊C为什么就不可以啊?B：have to可是解释是这样说的：题中有情态助动词may，故ACD三项都不对
问题描述：
If you can't finish the work before Friday ,you may ________work on the weekend .
选项有4个：A:must B:have C: have got to D:haven't to
为什么是选B啊C为什么就不可以啊?
B：have to
可是解释是这样说的：题中有情态助动词may，故ACD三项都不对
答
这里考的是情态动词的虚拟语气,may have done表示本来可以做而没做,句中解释为本来可以在双休日完成,其他选项完全不通,既不符合语法也不符合句意