Final answer:
Walden is depicted as a clear and tranquil pond that reflects its beautiful surroundings and reveals the treasures below its surface.
Step-by-step explanation:
Based on the passages provided, the appearance of Walden is described with a focus on its natural beauty and tranquility. The pond is characterized by its clear waters that enable one to see its depths and treasures below, as well as its serenity and reflective surface. The most accurate answer to the question 'What is the appearance of Walden?' is Option C: It is clear and reveals the treasures below. This description aligns with the depiction of Walden as a pristine location, set apart from the pollution and disturbances that characterize the industrial scenes described in some other passages. In these other descriptions, the presence of man-made elements or pollution often taints the scenery, contrasting with the unspoiled nature of Walden Pond. Therefore, the portrayal of Walden is one of purity and peace, a mirror-like surface reflecting the surrounding landscape.