加热炉风机突停将引起风机出口（）下降。
A、温度
B、真空度
C、负压
D、压力
参考答案：D
We should go out and stretch our legs. We ____ all day. [ ]
A. had sat
B. have been sitting
C. have sat
D. was sitting
我国2000年城镇人口与乡村人口的比例约为（）。
A．1:1
B．1:1.67
C．1:1.5
D．l:2
