The quality that makes the speaker "beautiful" in the last lines of the poem is C. He is beautiful because he is African American.
Langston Hughes's poem "I, Too, Sing America" addresses themes of racial identity, dignity, and the inherent beauty of African Americans, asserting their rightful place in the American narrative. The beauty referenced in the poem is tied to the speaker's identity and the strength that comes from embracing that identity in the face of discrimination and exclusion.