Which of the following is an example of a virus?

Norovirus is an example of a virus because it is a non-enveloped virus that is a leading cause of foodborne illness outbreaks. It primarily spreads through contaminated food or water, as well as through direct contact with infected individuals. Understanding the nature of Norovirus is crucial, as this virus can cause gastrointestinal illness characterized by symptoms such as vomiting and diarrhea.

In contrast, the other options listed represent bacteria rather than viruses. Bacillus cereus, Escherichia coli, and Clostridium botulinum are all bacterial pathogens associated with foodborne illnesses, but they function through different mechanisms and have different characteristics compared to viruses. Recognizing these distinctions enables better understanding of foodborne pathogens and aids in implementing proper food safety measures.