单项选择题
A.30° B.35° C.40° D.45°
A.15m以远 B.20m以远 C.25m以远 D.75m以远
A.1.50g/cm3 B.1.60g/cm3 C.1.70g/cm3 D.1.80g/cm3
A.105MPa B.70MPa C.35MPa D.21MPa
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