Children fall into three groups -- nontasters, regular tasters, and supertasters -- depending on how strongly they experience tastes. Supertasters strongly prefer mild cheddar cheese to sharp, regular tasters weakly prefer mild to sharp, and nontasters show no preference. Also, the more bitter a food tastes, the less children like it. Thus, supertasters experience sharp cheddar as tasting more bitter than mild cheddar, but nontasters experience sharp cheddar as tasting no more bitter than mild cheddar. Which one of the following, if assumed, enables the conclusion above to be properly inferred? ['The age of the child is the most important factor in determining whether that child is a nontaster, a regular taster, or a supertaster.', 'Supertasters like mild cheddar cheese more than do regular tasters.', 'Bitterness is the only factor relevant to how strongly children prefer sharp cheddar cheese to mild cheddar cheese.', 'Nontasters tend to like a wider variety of foods than do regular tasters, who in turn like a wider variety of foods than do supertasters.']