单项选择题
A.< 0.65B.< 0.60C.< 0.55D.< 0.50
A.< 0.5B.0.50~0.55C.0.55~0.60D.0.60~0.65
A.10B.20~25C.10~20D.15~20
A.15kN∕m3B.18kN∕m3C.10.78kN∕m3D.20.58kN∕m3
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