题目

There's someone knocking on the door. Who _____it be? —It must be Mary. She promised to be here at 8： 00 A. must   B. need    C. shall    D. can 答案：D第一节课：8∶10到8∶50；第二节课：9∶40到10∶20．每节课上(　　)分，课间休息(　　)分．