Soy Sauce has 1006 mg of Sodium

"This is what historians usually do, quibble about cause and effect when the point is, there are times when the world is in flux and the right voice in the right place can move the world."
-Orson Scott Card's Ender's Game

Which of the following must you obey over the other three
		A steady red light.
		A policeman.
		A stop sign.
		A flashing red light.

Policeman was my first guess but I thought it was a trick question!