Which of the following is an example of an indirect network effect?

Multiple choice question.

More teachers post lesson plans on an education platform, thus benefitting other teachers who post and search for lessons on the platform.

More marathon runners post details about upcoming marathons on a running platform, thus helping other runners who post on the platform find marathons to participate in$.$

More owners of a particular automobile brand post about the mechanical problems with their cars on an automotive platform, thus helping the other owners of that brand participating in the platform diagnose the issues with their cars.

There is an increase in the number of tennis coaches who post instructional videos on an online platform, thus attracting more tennis players to watch instructional videos on the platform, which in turn increases ad revenues for the coaches who post videos.