It has been announced that candidates ( 候选人)remain in their seats until all the papers has

问题补充：

It has been announced that candidates ( 候选人)remain in their seats until all the papers has been collected .

A. can

B. will

C. may

D. shall

答案：

A. can

B. will

C. may

(答案→)D. shall

解析：这里的shall表示一种命令；有必须、必将的意思。