The average level of fat in the blood of people suffering from acute cases of disease W is lower than the average level for the population as a whole. Nevertheless, most doctors believe that reducing blood-fat levels is an effective way of preventing acute W. Which one of the following, if true, does most to justify this apparently paradoxical belief? ["The progression from latent to acute W can occur only when the agent that causes acute W absorbs large quantities of fat from the patient's blood.", 'Several of the symptoms characteristic of acute W have been produced in laboratory animals fed large doses of a synthetic fat substitute, though acute W itself has not been produced in this way.', 'High levels of fat in the blood are indicative of several diseases that are just as serious as W.', 'The blood level of fat for patients who have been cured of W is on average the same as that for the population at large.']