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

d

The magnet induces a magnetic field in the paper.