Which of the following statements is true?
a. Energy as heat is transferred from a lower temperature to a higher temperature.
b. Energy as heat is transferred from a higher temperature to a lower temperature.
c. The amount of heat in a closed system is a constant.
d. Energy as heat transferred into an object is determined by the amount of work done on the object.

Refrigerant-134a flows through a carnot heat pump cycle at 0.5 kg/s. it is known that the maximum absolute temperature in the cycle is 1.1 times the minimum absolute temperature, and the net power input to the cycle is 2.5 kw. if the refrigerant changes from a saturated vapor to a saturated liquid during the heat rejection process, determine the maximum magnitude of the enthalpy of vaporization for this process in kj/kg (with 3 significant figures).