Final answer:
Malcolm X used the phrase 'sitting on a powder keg' to metaphorically describe the potential for violence among his listeners.
Step-by-step explanation:
Malcolm X said that his listeners are sitting on a powder keg as a metaphor for their potential for violence (c). He used this phrase to convey the idea that there was a high level of frustration, anger, and dissatisfaction among the Black community, which could potentially erupt into violent actions. Malcolm X believed that the constant oppression and acts of racism towards Black people could eventually lead to an explosive situation.