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 rate of change in mass of 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} )
• B. ( frac{ partial rho}{ partial t} )
• C. ( frac{ partial rho}{ partial t}(dx ,dy ,dz) )
• D. ([ frac{ partial( rho u)}{ partial x} + frac{ partial( rho v)}{ partial y} + frac{ partial( rho w)}{ partial z}]dx ,dy ,dz )