According to Stephen Prothero in Mencius and Xunxi played which of the following roles in Confucian history?
a. They were Legalist critics of Confucius
b. All these answers are correct
c. They were Mohist critics of Confucius
d. They were later followers of Confucius who worked to spread Confucius' teachings far and wide
e. They were two of the Three Great Sage-Kings whom Confucius is popularly believed to have resembled