问题
选择题
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
答案
答案：A
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。