The correct answer is B. A group of people interested in hearing an author speak
Explanation:
In sociology, collective behavior refers to an activity or behavior that implies the voluntary involvement of multiple individuals who commonly have a shared purpose and whose involvement is not regulated by any social institution, laws or conventions but is created in a spontaneous way. Considering this, the one that would be an example of collective behavior is "A group of people interested in hearing an author speak" because this describes a group of individuals rather than just one or two individuals that gather voluntarily, without the influence of a military, educational institution or law and who have a common interest, which in this case is a speech by an author.
