單項選擇題

如圖所示恒定流水箱,水頭H=5m,直徑d1=200mm,直徑d2=100mm,不計水頭損失。則粗管中斷面平均流速v1為:()

A.2.47m/s
B.3.52m/s
C.4.95m/s
D.4.35m/s