ThesmogarrivedintheYangtzeRiverDeltaregiononNov.30，

問題詳情：

The smog arrived in the Yangtze River Delta region on Nov.30，_________the air quality

    in 1 2 cities out of 25 was rated as severely polluted by Dec≯1

    A．where    B．when    C．which   D．what

【回答】

A

知識點：定語從句

題型：選擇題