In what way was Ralph Waldo Emerson important in Henry David Thoreau's professional life?

A. Emerson criticized Thoreau's work, which led to a long-standing rivalry.
B. Emerson was the one who paid Thoreau's poll tax, which freed him from prison.
C. Thoreau could not find a publisher for his books and relied on Emerson's influence.
D. Thoreau lived on Emerson's land, which was the subject of one of his books.