筛子声音异常的主要原因是筛机（）、相应配件螺栓松动、弹簧损坏。
参考答案：轴承磨损
We have too many people in our country. Their life will be ___________ if there are ___________ children in a family.
A．richer; fewer
B．poorer; fewer
C．richer; more
D．richer; less
率失真函数对允许的平均失真度是（）。
