It has been announced that candidatesremain in their seats until all the papers have been

问题补充：

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

A. can

B. shall

C. will

D. may

答案：

A. can

(答案→)B. shall

C. will

D. may

解析：考查情态动词的用法：shall用于规定，警告，命令，句意是：已经宣布了，考生在试卷收完前要坐在座位上。。选B。