Final answer:
Thoreau left the woods after completing his experiment of living a simple life, which he documented in 'Walden'.
Step-by-step explanation:
According to Walden, Thoreau leaves the woods because of c) Completion of his experiment. Thoreau's stay by Walden Pond was a purposeful experiment to live simply and to 'front only the essential facts of life'. He built his own cabin and subsisted thriftily to demonstrate the value of a simplified life, both materially and intellectually. After living for over two years in these conditions, Thoreau concluded his experiment, feeling that he had accomplished what he set out to do. Far from a lack of food or a desire for social interaction, and certainly not due to a fear of wild animals, Thoreau's departure was a calculated decision consistent with his philosophical aspirations.