Which of the following sentences demonstrates the proper use of a colon?

a. i am going to the store and will buy the following: apples, milk, bread, ice cream, and dog food.

b. the following: are my favorite foods ice cream, pizza, brussel sprouts and cheese.

c. i have all of these animals as pets dog: cat: hamster: gerbil: and a frog.

d. today: the mailman, the ups man, and the fedex truck all visited my house.