The rate of change of velocity along the depth of layer is ___________

• A. \(\frac{∂v}{∂z}=\frac{1}{γ_w}\frac{∂^2 \overline{u}}{∂z^2} \)
• B. \(\frac{∂v}{∂z}=\frac{k}{γ_w}\frac{\overline{u}}{∂z^2} \)
• C. \(\frac{∂v}{∂z}=\frac{∂^2 \overline{u}}{∂z^2} \)
• D. \(\frac{∂v}{∂z}=\frac{k}{γ_w} \frac{∂^2 \overline{u}}{∂z^2} \)