Identify the statement that is true about coal-bed fires.

A. They are extremely difficult to extinguish because fuel obviously is abundant and oxygen can enter easily, even through joints in surrounding rock.
B. They cannot start from spontaneous combustion; an "outside event" is necessary.
C. They are rare; worldwide, only a handful are currently burning.

If you could drill a hole straight to the center of the earth, and keep track of what the hole is going through, youwould find: a) you would go through one sort of material, and then a different, denser material, and then a still-different, still-denser material, because the planet is made of concentric layers, sort of like an onion. b) you would go through one sort of material all the way to the center, because the planet is all mixed up. c) if your hole started at the north pole, you would go through different layers of different materials, but ifyour hole started at the equator, you would go through one sort of material all the way to the center. d) if your hole started at the equator, you would go through different layers of different materials, but if yourhole started at the north pole, you would go through one sort of material all the way to the center. e) you would strike diet pepsi when you got to the center.