A climate-control heat pump can both heat and cool a building by 

A. moving heat energy from a low-temperature source to a
high-temperature sink.
B.moving heat energy from a high-temperature source to a
low-temperature sink.
C.moving heat energy either from a low-temperature source to a
high-temperature sink, or from a high-temperature source to a
low-temperature sink.
D.moving heat energy either from a low-temperature source to a
low-temperature sink, or from a high-temperature source to a
high-temperature sink.