The most appropriate response to the assassinations of Malcolm X and Martin Luther King Jr. would be B) There were protests in many neighborhoods.
Following the assassinations, there was widespread anger and grief within the African American community, which resulted in protests and demonstrations across various cities. The loss of these key figures led to significant unrest and calls for justice, highlighting the ongoing struggles against racial inequality and violence.
While the Black Panthers (A) were already formed in 1966 (before Malcolm X's assassination) and became more prominent afterward, the immediate response included protests. Option C about civil disobedience becoming more popular does reflect a broader context of the civil rights movement but isn't a direct response to their assassinations. Similarly, while marches were organized in various contexts, including later commemorative events, option D isn't specifically tied to the reactions at the time of their deaths.