Wordsworth's Tintern Abbey outlines several themes. Through the lines 1 to 49, the author describes the tranquility of the natural beauty. Indeed, the poem is about William's tour with his sister in Welsh Marhces. From lines 49 to 111, the poet describes the beauty of the landscape and in the remaining part of the poem, he writes about the bond between himself and his sister. We can see that nature is the main topic in Tintern Abbey. Therefore, the answer is C.