I’msorry,Bill.I

问题详情：

I’m sorry, Bill. I _________ the book to you last week, but I was so busy that I forgot to do so.

      A. must have returned                               B. could return  

       C. should have returned                            D. might return

【回答】

C

知识点：虚拟语气与情态动词

题型：选择题