Which of the following devices uses an outside energy source to transfer thermal energy from a cool area to a warm area? a. generator b. refrigerator c. battery d. electroscope

In nature, if something warm gets near a cool thing, then
some heat (thermal energy) ALWAYS moves AWAY from
the warmer thing TOWARD the cooler thing.  ALWAYS !
That's a Law of thermodynamics.

So how are we supposed to keep our ice cream frozen
and our soda cold, in a warm house ?

We get some smart scientists and engineers to figure out
how to fool nature, and how to move heat AWAY from a
cool place and TOWARD a warm place, in a small region.

Scientists and engineers did that for us a long time ago,
and now everybody uses it.  The thing is, we have to use
extra energy to move the heat in the direction is doesn't
want to go.

That's exactly what our REFRIGERATOR and FREEZER
do for us.  We plug them into an outlet, where they can get
electrical energy.  They use that energy to run motors and
fans and compressors, and somehow they make thermal energy
(heat) move in the un-natural direction ... away from soda that's
already cold and ice cream that's already frozen, out TOWARD
the warm kitchen.

therefore, the efficiency is: