Option d is the correct answer. The Dharma Chakra Pravartana ("The Turning Wheel of Law") is the first sermon that the Buddha gave after he attained enlightenment. In this sermon, the Buddha laid out the Four Noble Truths and the Noble Eightfold Path, the central teachings of Buddhism. Therefore, the concept of the Eightfold Path forms the theme of Dharma Chakra Pravartana Sutta. The Noble Eightfold Path is a practical guide to living a moral and ethical life.