问题补充:
-When should I hand in my paper?-It after class.
A. must be handed in
B. is handed in
C. was handed in
D. will hand in
答案:
(答案→)A. must be handed in
B. is handed in
C. was handed in
D. will hand in
解析:句意:我应该什么时候交卷?——下课后必须交。结合语境可知下文描述的是客观性动作,选项B只是陈述事实,语气不如选项A强烈,故选A.