Answer:
c. user; original equipment manufacturer
Step-by-step explanation:
When businesses buy and sell goods with one another, wherein one business's finished product can act as another business's input/component, such a marketplace is referred to as business markets.
A business shall be referred to as a user if it purchases goods from another business and subsequently uses those goods, which are not directly used in manufacture of it's own products.
An Original Equipment Manufacturer(OEM) refers to such a business which buys products which act as components or constitute a part of it's own product. In such a case, business buys such a part, uses it in manufacture of it's own product, makes necessary changes and then sells the whole product under it's own brand.