The most likely reason the author uses the word “sing” in the title of the poem is: 2. To Show that the speaker view himself as a legitimate voice in America.
In the poem, "I, Too, Sing America" Langston Hughes brought attention to the discrimination faced by the black people in America.
Just as singing can be regarded as a legitimate way of expressing oneself, the poet regarded himself as a legitimate voice that should also be heard in America.
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