单项选择题
A.0.5~1.5m∕sB.0.5~1.0m∕sC.0.1~0.5m∕sD.1.5~2.0m∕s
A.20%B.30%C.40%D.50%
A.0.65~0.75B.0.75~0.85C.0.85~0.95D.0.95~0.98
A.50%~60%B.60%~70%C.70%~80%D.80%~90%
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