Which of the following shellfish are most likely to cause illness?

Oysters are considered the shellfish most likely to cause illness due to their method of feeding and their habitat. They filter seawater to obtain nutrients, which makes them susceptible to accumulating harmful microorganisms such as bacteria, viruses, and toxins present in contaminated waters. Vibrio vulnificus and Norovirus are two common pathogens associated with oyster consumption, especially if they are eaten raw or undercooked.

Additionally, the environments where oysters are harvested often have higher levels of pollution, which can also contribute to the potential for illness. This risk is heightened during certain times of the year, particularly warmer months when water temperatures rise, and pathogens are more prevalent.

Crabs, shrimp, and lobsters can also be involved in foodborne illnesses, primarily if they are mishandled or undercooked; however, the association of oysters with illness is more significant primarily due to their unique feeding behavior and environmental vulnerabilities. Therefore, the option indicating oysters is correct as they have a well-documented history of being linked to seafood-related illnesses.