教室CO2浓度测定点应为（）。
A.教室讲台处
B.教室靠窗处
C.教室侧墙处
D.教室中央点
E.教室后墙处
参考答案：D
Yang Jiazheng_____a book about Shuangqiao village last year but I don't know whether she has finished it.
A．has written
B．wrote
C．had written
D．was writing
1/6，1/3，2/3，4/3，( )
A．8/3
B．2
C．9/8
D．2/3
