Joule - Thomson coefficient is given by:

• A. \({\left( {\frac{{\partial p}}{{\partial T}}} \right)_h}\)
• B. \({\left( {\frac{{\partial T}}{{\partial h}}} \right)_p}\)
• C. \({\left( {\frac{{\partial h}}{{\partial p}}} \right)_T}\)
• D. \({\left( {\frac{{\partial T}}{{\partial p}}} \right)_h}\)