Final answer:
The Hudson River School's subject matter was influenced by the Romantic emphasis on the sublime beauty of nature, reflecting a spiritual connection with the American landscape through expansive paintings.
Step-by-step explanation:
The aspect of Romantic thought that contributed to the Hudson River School's choice of subject matter was B. Emphasis on the sublime beauty of nature. The Hudson River School was the most influential landscape art movement in 19th century America, characterized by its artistic creations that focused on the majesty and power of the natural world.
The movement was a cultural response to industrialization, celebrating the unspoiled American landscape as a source of spiritual renewal and national pride. Its founders and followers, like Thomas Cole and Albert Bierstadt, were inspired by Romanticism's reverence for nature and sought to capture its overwhelming presence through their artworks. They also reflected the political themes of America during that period, such as discovery, exploration, and settlement, in their expansive landscape paintings.