Threadless, a T-shirt manufacturing company, relies on the contribution of online community members in the design process. The community includes a group of volunteer designers who submit designs and vote on the designs submitted by others. In addition to free exposure, designers receive monetary incentives, including a $2,500 base award as well as a percentage of T-shirt sales. These incentives allow Threadless to encourage continual customer contribution. This serves as an example of:

A.patent.
B.social network.
C.process innovation.
D.licensing.
E.user-led innovation.