A group of veterinarians at a major veterinary hospital was interested in investigating a possible link between enteroliths, stones that form in the colon of horses, and diet. They decided to conduct a survey of feeding practices of horses in the hospital's state. They created a survey questionnaire and decided to administer it to the owners of every fifth horse being treated at the hospital. The population of interest is: A. all horses brought to the clinic. B. all horses in the state. C. all horses that are diagnosed with enteroliths. D. None of the answer choices is correct.