A.74.25cm油柱 B.74.25mH2O C.95.26cm油柱 D.62.26m油柱
半圓形明渠如圖所示,半徑r0=4m,其水力半徑R為:()
A.4m B.3m C.2.5m D.2m
A.54632 B.67653 C.76335 D.84892