单项选择题
A.1/3 B.2/3 C.1/4 D.3/4
A.50 B.100 C.150 D.200
A.1/10~1/100 B.1/20~1/200 C.1/30~1/300 D.1/40~1/400
A.砂 B.粉砂 C.细砾 D.黏土
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