Which of the Following Is Not an Example of a Market

Which of the following is not an example of a market?

A) A cattle auction, where farmers and ranchers bring cattle to be purchased by packing plants
B) Etsy.com, a Web site where artists, designers, and craftspersons offer items they have made to interested buyers
C) A city requires homeowners to pay $500 for putting in a sidewalk on their street
D) The National Residency Matching Program, where medical residents express their preferences for residencies, hospitals express their preferences for medical residents, and these preferences are used to match residents to residencies