Concept:The phrase “too ... to” means “excessively ... to,” and it is correctly intensified by “much.”Explanation:The sentence needs the meaning “too sour to be eaten.”The correct intensifier before “too” is “much,” not “more.”“More too” and “more so” are not used correctly with an adjective like “sour.”Therefore, the correct phrase is “much too sour to be eaten.”Answer:C. much too