Which of the following describes a way in which bacteria are harmful to humans?

A. Some vitamins, such as vitamin K, are made by bacteria in the human gut.
B. Some common foods, such as yogurt and Swiss cheese, are made using bacteria.
C. Some human diseases, such as cholera and dysentery, are caused by bacteria.
D. Some medicines, such as erythromycin and tetracycline, are made by bacteria.