单项选择题
A.60% B.70% C.80% D.90%
A.3m/min B.5m/min C.8m/min D.10m/min
A.1/2 B.1/3 C.1/4 D.1/4
A.0.2~0.3m B.0.3~0.4m C.0.4~0.5m D.0.5~0.6m
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