1/59,3/70,5/92,7/136,()
A.9/272
B.1/224
C.9/224
D.11/224
参考答案:C
With so much noise of the traffic, I couldn't________and do my research work.[ ]
A. put down
B. settle down
C. break down
D. take down
什么叫滤料"有效粒径"和"不均匀系数"?"不均匀系数"过大对过波、和反冲洗有何影响?