Concept:The phrase directly compares abstract ideas to a physical object, so it is a metaphor.Explanation:"The flag of knowledge and morality" is not a literal flag.It means that teachers, through their work, proudly display or advance knowledge and morality.This comparison is direct and does not use "like" or "as."Therefore, it is a metaphor, not a euphemism, litotes, or metonymy.Answer:C. metaphor