题目

According to the air traffic rules, you______switch off your mobile phone before bearding. A. may                                B. can                                   C. would                             D. should 答案：D 解析: 此题考查情态动词的用法。根据句意“按照空中交通规则，你应当在登机前关掉你的手机”，所以只有should(应该，应当)符合题意。

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