Final answer:
Cooking fish and oysters in the same fryer oil can cause cross-contact of allergens. The best hypothesis for the cause of the illness from eating oysters is bacterial contamination. Experimental controls help isolate variables in an experiment.
Step-by-step explanation:
True, cooking both fish and oysters in the same fryer oil can cause cross-contact of allergens. This means that proteins from the fish can mix with the oysters, potentially causing allergic reactions in individuals sensitive to fish if they consume the oysters without knowing they've been cooked in the same oil.
Regarding the statement that best describes why a number of people became ill after eating oysters in a restaurant, statement e, 'Bacteria in the oysters may have caused the illness,' is likely the best hypothesis. This statement suggests a scientifically testable cause for the sickness, whereas the other statements are observations (a, b, c) or an irrelevant sentiment (d).
Experimental controls are necessary in testing hypotheses to isolate the effects of a single variable, ensuring that the outcome of the experiment is due to the variable being tested rather than other factors. This helps in accurately determining whether the bacteria in the oysters were the cause of the illness.