It has been announced that candidates remain in their seats until all the papers have be

问题补充：

It has been announced that candidates remain in their seats until all the papers have been collected.

A. can

B. will

C. may

D. shall

答案：

A. can

B. will

C. may

(答案→)D. shall

解析：shall用于陈述句的第二、第三人称时，表示说话人的意图、允诺、警告、命令、决心等，意思是“必须，应，可。”这句话的意思是：据宣布，考生在收卷前必须坐在自己的座位上。