Which of the four fundamental forces of nature is responsible for keeping you on the earth's surface?
A. The strong force
B. The weak force
C. The electromagnetic force
The intended answer is D, gravity. However, this is not correct. We are kept on the earth's surface by two forces: gravity presses us down, but we are also prevented from falling through to the centre of the earth by electromagnetic forces between atoms in the ground. It is the balance between these two forces that keeps us on the earth's surface. It's very easy to take for granted the solidity of the ground we walk on.
The quiz question could easily be fixed by inserting the word "down" thus:
Which of the four fundamental forces of nature is responsible for keeping you down on the earth's surface?