An agglomeration of men presents new characteristics very different from those of the individuals composing it. The sentiments and ideas of all the persons in the gathering take one and the same direction, and their conscious personality vanishes. A collective mind is formed, doubtless transitory, but presenting very clearly defined characteristics. The gathering has thus become what, in the absence of a better expression, I will call an organized crowd. . . . It forms a single being . . .” Which theory describes this quote? A. mass society theory B. public goods dilemma C. tragedy of the commons D. contagion theory

The Contagion Theory is a theory about the collective behavior of human beings. In short, it holds that the behaviors, ideas or mood of a group of people can be transferred to other individuals, even if those features are unreasonable and inconsistent with the individual's personality or behavior. However, this effect is temporary, because once the individual leaves the crowd, the effect goes away. The theory suggests that the crowd is "contagious": it exerts a hypnotic influence on their members because people have a habit of following the crowd, just like it happens in the quote.