---I haven’t got the reference book yet but I’ll have a test on the subject next month. -

问题补充：

---I haven’t got the reference book yet, but I’ll have a test on the subject next month.

---Don’t worry. You have it by Friday.

A. could

B. shall

C. must

D. may

答案：

A. could

(答案→)B. shall

C. must

D. may

解析：考查情态动词。Could能够，用于过去时态或虚拟语气；shall用于二三人称表示应该，必须；must 必须，一定；may 可以，语气较弱。句意：我还没有拿到参考书，但是我下个月有一次这个科目的考试。——不要担心。你星期五之前应该能拿到。故选B。