Which of the following is a cause of foodborne disease?

Foodborne diseases are often caused by the consumption of contaminated food. When food comes from an unknown source, it carries the risk of being unsafe or contaminated with harmful bacteria, viruses, or parasites. This lack of traceability means that there are no guarantees about how the food was handled, prepared, or stored, which can lead to significant health risks for consumers.

It is important to understand that the other choices do not directly cause foodborne illness in the same way. Excessive cooking temperatures can actually help kill harmful pathogens, while unopened foods are generally safe, assuming they are within their expiration dates and stored properly. High salt content in food does not lead to foodborne diseases, though it can have other health implications. Therefore, receiving food from an unknown source is a notable risk factor for foodborne diseases due to the uncertainty of its safety standards.