ThesmogarrivedintheYangtzeRiverDeltaregiononNov.30，

问题详情：

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

知识点：定语从句

题型：选择题