The legend states that Adi Shankaracharya chose Sringeri as the site for his first matha after witnessing a remarkable sight - a snake spreading its hood to protect a pregnant frog from the scorching sun. This sight of natural enemies showing compassion exemplified the peaceful, non-violent atmosphere suitable for a spiritual institution. Option A (cool atmosphere) and Option B (serene atmosphere) describe generic features but not the specific legendary reason. Option D (orders of guru) is incorrect - the choice was his own, inspired by this vision.