When Cullen speaks of planting while others reap, the standing "abject and mute," he is speaking about the (racial, internal or casual) injustice present in American society

A and B

Explanation: When Cullen speaks of planting while others reap, and standing "abject and mute," he is speaking about the racial injustices present in American society. As these injustices have changed over time, the American identity has also shifted. Those changes are, in turn, reflected in American literature.