Suppose that you found out that none of the products sold by ACME have a warranty. Which of the following must be true (which conclusion follows validly)?
a. Everything that's not a product sold by ACME has a warranty.
b. Some products not sold by ACME do have a warranty.
c. Some products sold by ACME do not have a warranty.
d. Nothing with a warranty is a product sold by ACME.