Which of the following is an example of a consumer$-$to$-$consumer $($C$2$C$)$ e$-$marketplace?

An airline gives a traveler best travel and ticket offers in response to the traveler's post on the airline's website that she wants to fly from New York to San Francisco.

An author who writes book reviews, posts links to books on

Amazon.com on her website, and receives revenues from successful sales to her blog subscribers.

A person posts information about furniture he wishes to sell on eBay and sells it to another individual who views that eBay page.

A business owner calculates the tax he has to pay to the IRS through an interactive tool on its website and makes the payment via wire transfer from the same site.