Final answer:
Martin Luther King Jr. uses an extended metaphor to compare a bad check to the unfulfilled promise of freedom and equality for African Americans. He believes that America has given African Americans 'a bad check' by failing to fulfill its promises of freedom and equality.
Step-by-step explanation:
Martin Luther King Jr. uses an extended metaphor in his famous speech titled 'I Have a Dream' to compare a bad check to the unfulfilled promise of freedom and equality for African Americans in America. He develops this metaphor by highlighting the discrepancy between the promise of equality in the country's founding documents and the ongoing discrimination faced by African Americans. According to King, America has given African Americans 'a bad check' by failing to fulfill its promises of freedom and equality.