39. On a thermodynamic P-V (pressure-volume) diagram, comparing the slope of the curve for an adiabatic process to that of an isothermal process (assuming the gas expands), which of the following is correct? (A) The adiabatic curve is steeper (has a greater absolute slope). (B) The isothermal curve is steeper (has a greater absolute slope). (C) The slopes are the same. (D) It depends on the type of gas.