What is the best example of biological contamination?
a. a wedding ring that falls off of a food worker's finger and into the salad dish.
b. a can of pesticide is sprayed over the food prep area currently in-use.
c. a sick food worker coughs onto a prepared sandwich.
d. a wrapper for uncooked meat comes in contact with ready-to-eat tomatoes?

The correct answer is C. A sick food worker who is sick may be suffering from an infectious disease. If such a person coughs into the food she is preparing, the infectious agent in her system may come out with the saliva drops and land on the food. Any one who eat such food will automatically get the disease too. 
Biological contamination occurs when micro organisms or other toxins contaminate food.