What is the title of Henry David Thoreau's work that reflects on simplicity and contemplation in nature?

Henry David Thoreau's work titled "Walden" is a profound reflection on simplicity, self-sufficiency, and the importance of nature in human life. Written during his time living in a small cabin near Walden Pond, Thoreau emphasizes the idea of simplifying one’s life to focus on personal contemplation and connection with the natural world. The book serves as both a narrative of his experiment in living deliberately and a philosophical text that critiques the complexities of modern society and materialism. It’s a foundational work in American literature and aligns closely with transcendentalist beliefs, encouraging readers to find beauty and meaning in solitude and nature. This makes "Walden" the correct choice in relation to the themes of simplicity and contemplation.

The other options do not encapsulate these central themes as effectively. "Nature's Call" is not a well-known work by Thoreau, "The Seasons" is typically associated with other authors like James Thomson, and "On the Duty of Civil Disobedience" focuses primarily on Thoreau's views regarding government and individual morality rather than his reflections on nature and simplicity.