The answer is "Εμπεδοκλής" because the question asks for the philosopher who proposed the theory of "perception as a guide to truth." Among the three options given, Empedocles is the philosopher who believed that our senses are reliable sources of knowledge and that perception is a valid way to understand the world. Parmenides, on the other hand, argued that true knowledge can only be gained through reason and logic, while Thales focused on the natural world and the concept of water as the fundamental element. Therefore, the correct answer is Empedocles.