A system performs work $∆\mathrm{W}$ when an amount of heat $∆\mathrm{Q}$ is added to the system. The corresponding change in the internal energy is $∆\mathrm{U}$. A unique function of initial and final
states irrespective of the mode of change is: 

• A

  $∆\mathrm{W}$

• B

  $∆\mathrm{Q}$

• C

  $∆\mathrm{W} \mathrm{and} ∆\mathrm{Q}$

• D

  $∆\mathrm{U}$