Which of the following cases is the BEST example of an instance of social contagion? 

A person is suffering from a severe injury on the side of the road. However, people driving by fail to stop to help even though they notice the injured person. 

A teacher in a school smells gasoline and begins to feel nauseous; soon most of the school's population is also feeling nauseous. Later, it is discovered that there was never a gas leak. 

A politician gives a very moving speech in which he argues.