单项选择题
A.30° B.35° C.40° D.45°
A.2m B.1m C.2.5m D.0.8m
A.0.8m B.1.2m C.1.5m D.2.0m
A.40~65N/m B.20~30N/m C.30~40N/m D.70~80N/m
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