单项选择题
A.≥2m/hB.≥3m/hC.≥5m/h
A.5% B.10% C.15%
A.1.3g/cm3 B.2.0g/cm3 C.3.0g/cm3
A.1.00g/cm3 B.1.70g/cm3 C.2.70g/cm3
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