分类：教育/科学-外语学习
问题：高二英语选择题sorrysir,icantanswerthequ 
sorry sir,i cant answer the questn---well you are supposed ____ the part of historya to be readingb to readc having readd to have read答案选择d为什么
回答：be supposed to do是固定词组,应该做某事
此题也可以等效于you should have read the part of history,
其中should have done 是情态动词的一种特殊用法,表示本应该做某事而实际上没做,同样shouldn't have done表示本不应该做而实际做了