A magnet can hold a piece of paper to the door of a refrigerator. How does the magnet stick without touching the door?

a
The magnet induces a magnetic field in the paper.
b
Gravity attracts the magnet to the door.
c
The magnetic field of the magnet can act at a distance, and influence the metal of the door through the paper.
d
Friction attracts the paper to the magnet.

c

The magnetic field of the magnet can act at a distance, and influence the metal of the door through the paper.