单项选择题
A.1.1~1.3B.1.2~1.4C.1.3~1.5D.1.4~1.6
A.1.5B.2.0C.2.5D.3.0
A.0.5m∕minB.1.0m∕minC.1.5m∕minD.2.0m∕min