单项选择题
A.1~2倍B.2~3倍C.3~5倍D.4~6倍
A.1~2B.2~3.5C.3~5D.4-6
A.2~3m/sB.3~5m/sC.5~8m/sD.8~10m/s
A.1:0.5~1:1B.1:1~1:2C.1:1.5~1:3D.1:3~1:4
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