问题
选择题
It worried her a bit _____ her hair was turning grey. [ ]
A. while
B. that
C. if
D. for
答案
答案：B
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It worried her a bit _____ her hair was turning grey. [ ]
A. while
B. that
C. if
D. for
答案：B
)对河水、湖水消毒是城市饮水处理的新技术。已知反应为: 
,下列说法正确的是
既是氧化剂又是还原剂