Final answer:
The best speech excerpt containing a metaphor that illustrates the suffering of Black people and aligns with Hector's topic sentence is the line that speaks of moving from 'the quicksands of racial injustice to the solid rock of brotherhood.'
Step-by-step explanation:
Hector's topic sentence states that Dr. Martin Luther King Jr.'s "I Have a Dream" speech utilizes numerous metaphors to depict the suffering of Black people. The best excerpt from the speech that supports this topic sentence is (a) "Now is the time to lift our nation from the quicksands of racial injustice to the solid rock of brotherhood." This metaphorical language vividly illustrates the transition from an unstable, treacherous state to one of unity and strength.