The boundary layer flow over a flat plate with zero pressure gradients is shown in Figure 44.The control volume is defined as dashed line a-b-c-d and the depth is defined as w. Ahead ofthe plate the velocity is uniform, U. The velocity distribution across cd is approximated by   , here δ(x) denotes the boundary layer thickness. Which of thefollowing statements is correct? 
(A) the mass flux across bc equals  /5,
(B) the mass flux across ab equals -  ,
(C) the mass flux across cd equals2  /3  ,
(D) the mass flux across bc equals   /3.