What is the primary function of a heat pump? $($recommended time $1$ min, $2$ points$)$

a$.$

To maintain constant entropy during a process

b$.$

To remove waste heat from a system without work input

c$.$

To convert heat into work efficiently

d$.$

To operate as a reversible heat engine

e$.$

To transfer heat from a low$-$temperature medium to a high$-$temperature medium