The best answer is D
A freely suspended magnet will always point in the North - South direction in the absence of any other magnet. This suggests that the earth itself behaves as a magnet which causes a freely suspended magnet (or magnetic needle ) to point always in a particular direction namely North and South.
The south pole of the earth's magnet is in the geographic north because it attracts the north pole of the suspended magnet and vice versa. However it is important to note that the position of earth's magnetic poles are not well defined because they are spread over an area.
Answer:
B) A difference in pressure across a distance.
