Final answer:
Emperor Wu (Wudi) of the Han Dynasty advocated following Confucianism, marking a significant period where Confucian philosophy began to establish its influence within the empire.
Step-by-step explanation:
The Han Dynasty emperor who advocated the following of Confucianism was Emperor Wu (Wudi), identifiable as option A in the provided question. During his reign, Emperor Wu was influenced by Confucian scholars, although he was known to have varied interests, including in Daoism and Legalism, and did not always follow the guidance of Confucian advisors. Nevertheless, Confucianism began to gain a more substantial foothold during his reign. It's important to note that while Confucian scholars had limited influence during their lifetimes, their writings had a lasting impact, which contributed to the eventual establishment of Confucianism as an essential philosophy in the Han empire.