The energy density $\frac{U}{\mathrm{V}}$ of an ideal gas is related to its pressure P as

• A

  $\frac{U}{\mathrm{V}} = 3\mathrm{P}$

• B

  $\frac{U}{\mathrm{V}} = \frac{3}{2}\mathrm{P}$

• C

  $\frac{\mathrm{U}}{\mathrm{V}} = \frac{1}{3}\mathrm{P}$

• D

  $\frac{U}{\mathrm{V}} = \frac{2}{3}\mathrm{P}$