单项选择题
A.绿灯 B.黄闪 C.绿闪 D.白灯
A.40m±15m B.50m±15m C.45m±15m D.45m±10m
A.5km/h B.6km/h C.7km/h D.8km/h
A.10s B.20s C.30s D.40s
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