： 适用于圆形直管的不可压缩流体流动的连续性方程（ ）。A:u1d1= u2d2= ······= u d B:u1d12 = u2d22 = ······= u d2 C:u1ρ1= u2ρ2=······= u ρ D:u1Aρ1= u2Aρ2=······= u Aρ 答案: u1d12 = u2d22 = ······= u d226、