Blank (i)
Context: Hughes's expression of Black folk culture established his writing as a (i) _______ in the history of African American literature.
- The phrase "established his writing as a ______ in the history" requires a word meaning a turning point, a prominent feature, or a significant position.
- C. landmark (An important stage or turning point of an era or event) fits perfectly, conveying the historical significance of his work.

Blank (ii)

Context: "most of his folk poems have the (ii) ______ marks of this folk culture's oral tradition."
- The poems display the recognizable features ("marks") of the oral tradition.
- D. distinctive (Characteristic of one person or thing, and so serving to distinguish it from others) is the best choice, indicating that the poems clearly bear the identifying traits of that culture.

Blank (iii)
Context: The final part of the passage sets up a contrast: the poems seem artless, but they were actually "carefully and artfully crafted." Hughes, however, insisted his poetry was not artfully constructed. Therefore, the word in the blank must describe a spontaneous or unstudied approach.
- Hughes prided himself on being an (iii) ______ and impressionistic writer of poetry.
- H. impromptu (Done without being planned, organized, or rehearsed) directly aligns with his claim that his work was "not an artfully constructed poetry" and reinforces the idea of "artlessness."