单项选择题
A.50mm B.25mm C.13mm D.6mm
A.25mm圆孔筛 B.50mm圆孔筛 C.50mm方孔筛 D.25mm方孔筛
A.11.50% B.17.50% C.12.00% D.18.00%
A.1/2 B.1/3 C.1/4
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