An Adiabatic Free Expansion of a Gas in a Thermally

Multiple Choice

An adiabatic free expansion of a gas in a thermally isolated container is not reversible because

A) work must be done on the gas to return it to its original volume.
B) heat must be exchanged with the surroundings to return the gas to its original temperature.
C) its internal energy has a greater value after the expanded gas is returned to its original volume and temperature.
D) of all of the above.
E) of (a) and (b) above only.