A gas is heated at constant pressure. The fraction of heat energy used to increases the internal energy of the gas molecules is

• A

  $\mathrm{\gamma }$

• B

  $1/\mathrm{\gamma }$

• C

  ${\mathrm{C}}_{\mathrm{p}}-{\mathrm{C}}_{\mathrm{v}}$

• D

  ${\mathrm{C}}_{\mathrm{p}}+{\mathrm{C}}_{\mathrm{v}}$