泥龄法是通过控制系统的（）最佳来使处理系统维持最佳运行效果的方法。
A.活性污泥浓度
B.污泥停留时间
C.污泥颗粒大小
D.细菌含量
参考答案：B
已知f(x)为奇函数，当x∈(-∞，0)时，f(x)=x+2，则f(x)＞0的解集为[ ]
A．(-∞，-2)
B．(2，+∞)
C．(-2，0)∪(2，+∞)
D．(-∞，-2)∪(0，2)
Great changes __________ in China in the past few years.
A． were taken place
B． took place
C． have been taken place
D． have taken place
