It has been announced that all the students put on 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：句意：已经宣布所有的学生在上学前要戴面具以防感染SARS病毒，表示：规定或法律条文等用shall 语气强烈，will“意愿”，need“需要”，may“可以”，选A。