A heat pump and heat engine are being developed. The heat pump takes the heat from the environment at 10C and gives it to the heat source at 65C. The heat drawn from the heat source at 65C is used to operate the heat engine. This heat engine also produces power and transfers its heat to the environment at 10C. What is the maximum efficiency of this combined system?

A) 25%
B) 50%
C) 75%
D) 100%