20． -- I’m terribly sorry that I missed your birthday part． I just completely forgot．

-- Oh, ______

A． that’s all right　　　　　　　　　　　　　　 B． take it easy

C． don’t mention it　　　　　　　　　　　　　 D． that’s right

19． You did turn in your report on time, but it ______ better, you know．

A． could be done　　　　　　　　　　　　　　　　　　 B． must be done

C． could have been done　　　　　　　　　 　　　 D． must have been done