A.0.025 B.0.0335 C.0.0262 D.0.041
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