问题描述：
能给分析下这道题选shall的原因吗
27.It has been announced that candidates ____B__D____ remain in their seats until all the papers have been collected.（02 上海）
A.can B.will C.may D.shall
27.It has been announced that candidates ____B__D____ remain in their seats until all the papers have been collected.（02 上海）
A.can B.will C.may D.shall
问题解答：
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