定容比热 $C_V$ 等于

1. A

   $\left(\frac{\partial U}{\partial T}\right)_V$

   正确
2. B

   $\left(\frac{\partial i}{\partial T}\right)_p$

3. C

   $\left(\frac{\partial p}{\partial T}\right)_V$

4. D

   $\left(\frac{\partial V}{\partial T}\right)_p$