6. If three identical samples of an ideal gas are taken from initial state I to final state F along the paths IAF, IF, and IBF as shown in the pV -diagram above, which of the following must be true?
(A) The heat absorbed by the gas is the same for all three paths.
(B) The change in internal energy of the gas is the same for all three paths.
(C) The expansion along path IF is adiabatic.
(D) The expansion along path IF is isothermal.