Scientists have long thought that omega-3 fatty acids in fish oil tend to lower blood cholesterol and strongly suspected that a diet that includes a modest amount of fish would provide substantial health benefits. Now these views have acquired strong support from a recent study showing that middleaged people who eat fish twice a week are nearly 30 percent less likely to develop heart disease than are those who do not eat fish. Which one of the following is an assumption required by the argument? ['The test subjects in the recent study who ate fish twice a week did not have a diet that was otherwise conducive to the development of heart disease.', 'The test subjects in the recent study who ate fish twice a week were no more likely than those who did not to have sedentary occupations.', 'The test subjects in the recent study who did not eat fish were significantly more likely to eat red meat several times per week than were those who did eat fish.', 'The test subjects in the recent study who ate fish twice a week were not significantly more likely than those who did not to engage regularly in activities known to augment cardiorespiratory health.']