It has been announced that all the students put on the masks before going to school in case they are infected with SARS virus.
A. shall
B. will
C. need
D. may
网友回答
(答案→)A. shall
B. will
C. need
D. may
解析：考查情态动词的用法：shall用于第二，第三人称表示允诺，警告，规定，句意：已经宣布所有的学生在上学前要戴口罩以免感染Sars病毒。选A。