在差动放大电路，下列说法中，不能提高共模抑制比方法是（）。
A、电路的对称性好
B、Re的接入
C、采用恒流源取电阻Re
D、采用正负电源供电
参考答案：C
工程实践证明，如果水灰比大于（），则混凝土抗渗性能将急剧下降。
A．0．5
B．0．55
C．0．6
D．0．65
"In the past we were a lonely car maker, but we had good business," says Bernd Engelstadter, technical executive director at Shanghai Volkswagen, adding to he arrived in China seven years ago "competition was not a problem".
A．that
B．when
C．that when
D．when that
