For hundreds of years, people have been using the Chinese invention called the compass.1 People use a compass to find the right direction at sea. A compass uses the pull of a magnet to show which direction is north and which is south. But it does not use a small magnet; it uses the Earth itself. The Earth functions like a magnet, and like all magnets it has a north pole and a south pole. A compass uses a magnetized needle. The north pole of the compass needle is pulled toward the south pole of Earth, while its south pole is pulled towards the Earth's North Pole.2 So the compass needle always points north-south. 1. Patrick Bentley, Foundation of the Earth (New York: Penguin Random House, 1985), 183.

2. Karen McGill and Jeffrey Adams, "Magnets," The Foundation of Natural Sciences, last modified 12 July 2011, Harry is working on a report about the various uses of magnets. He adds footnotes to show which sources he used to do his research. According to the second footnote notation, what kind of source has Harry used?
A.
a short story
B.
an interview
C.
an encyclopedia
D.
a web page