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  • 科目:英语
  • 题型:单选题
  • 难度:中等
  • 人气:150

Beijing was under an “orange” smog alert on Feb. 24, which marks the first time the second-highest warning level of a new system introduced last year________.

A.has been raised B.raised
C.has risen D.rose
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Beijingwasunderanorangesmogale