Buyline is an e$-$commerce Web site. It has come up with a promotional offer where buyers get a $60$ percent discount on refrigerators if a minimum of $100$ buyers agree to buy the product within $24$ hours of the offer being announced. In this case, it is evident that BuyLine is a

social networking site

group buying platform

peer$-$to$-$peer e$-$commerce platform

participatory e$-$commerce site