A desk.
A commodity is actually a good or a service. A service is a something that can be performed (is an action) and is not something tangible or something concrete that can actually be touched. A swimming lesson is an action. Walking a dog is an action. House cleaning is an action. Therefore, all of these things are services. A good is a tangible product that is concrete—something that is physical and can be touched. Out of all of the options, a desk is the only commodity that is a good.