On a summer day, you keep the air conditioner in your room running. From the list numbered 1 to 4, choose the hot reservoir and the cold reservoir.

1. The air outside
2. The compartment inside the air conditioner where the air is compressed 

3. The freon gas that is the working substance (expands and compresses in each cycle) 

4. The air in the room
(a) 1 is the hot reservoir, 2 is the cold reservoir.
(b) 1 is the hot reservoir, 3 is the cold reservoir.
(c) 1 is the hot reservoir, 4 is the cold reservoir.
(d) 2 is the hot reservoir, 3 is the cold reservoir.
(e) 2 is the hot reservoir, 4 is the cold reservoir.
(f) 3 is the hot reservoir, 4 is the cold reservoir.