Consider an infinitesimally small fluid element with density (of dimensions dx, dy and dz) fixed in space and fluid is moving across this element with a velocity ( vec{V}=u vec{i}+v vec{j}+w vec{k} ). The net mass flow across the fluid element is given by ______

• A. ([ frac{ partial( rho u)}{ partial x} + frac{ partial( rho v)}{ partial y} + frac{ partial( rho w)}{ partial z}]dx ,dy ,dz )
• B. ([ frac{ partial( rho u)}{ partial x} + frac{ partial( rho v)}{ partial y} + frac{ partial( rho w)}{ partial z}] )
• C. [ ]dx dy dz
• D. ([ frac{ partial( rho)}{ partial x} + frac{ partial( rho)}{ partial y} + frac{ partial( rho)}{ partial z}]dx ,dy ,dz )