【题目】It has been announced that all the students ________ put on masks before going to school in case they are infected with SARS virus.
A. shallB. willC. needD. may
在线课程【答案】A
【解析】
考查情态动词。句意：所有学生们应在去学校之前带上口罩以防感染非典病毒，这已经被宣布。shall用于第二、第三人称，表示说话人给对方命令、警告、允诺或威胁，故选A项。