The partial differentiation of velocity of water in soil element with respect to depth z in terms of coefficient of volume change is given by ____________

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