Which of the following statements is true of an express warranty?

a$.$

It prohibits other firms from using a brand or part of a brand without permission

b$.$

It is an unwritten guarantee that a good or service is fit for the purpose for which it is sold

c$.$

It is a written guarantee that the product or service being sold is fit for the purpose for which it is sold

d$.$

It gives the impression of environmental friendliness to a product