What Is Threat of Substitute Products or Services

What is threat of substitute products or services?

A) the ability of buyers to affect the price they must pay for an item
B) the suppliers' ability to influence the prices they charge for supplies (including materials, labor, and services)
C) high when it is easy for new competitors to enter a market and low when there are significant entry barriers to joining a market
D) high when there are many alternatives to a product or service and low when there are few alternatives from which to choose