In Michael Porter's Five Forces Model,the Threat of Supplier Bargaining

In Michael Porter's five forces model,the threat of supplier bargaining power refers to:

A) a buyer being large enough,to affect a selling company's performance.
B) the likelihood a supplier will enter into a customer's market.
C) visiting competitors to learn about their customer service and their products.
D) vying for the supplier's dollar.
E) the threat of substitute products.