The quality of unrefined olive oil is not actually defined in terms of acidity, yet extensive tests have shown that the less free oleic acid an unrefined olive oil contains per liter, the higher its quality. The proportion of free oleic acid that an olive oil contains is an accurate measure of the oil' s acidity. If the statements above are all true, which of the following conclusions is best supported by them ? ['Free oleic acid is the only acid that unrefined olive oil contains.', 'When an olive oil is refined, the concentration of oleic acid in the oil is reduced.', 'The quality of an unrefined olive oil can be determined only by accurately measuring its acidity.', 'If an unrefined olive oil is intermediate in acidity between two other unrefined olive oils, it will also be intermediate between them in quality.']