单项选择题
A.45mm,1% B.50mm,2% C.45mm,2% D.50mm,1%
A.95% B.85% C.90%
A.1%~2% B.3%~4% C.5%~6%
A.暗沟 B.盲沟 C.泄水槽 D.渗沟
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