Which of the Following Helped Crystalize a Distinct Chinese Identity

Which of the following helped crystalize a distinct Chinese identity by 1300?

A) Buffer states such as the Khmer protected the Chinese heartland from outside invasion or contacts.
B) Song dynasty printed books established classical Chinese as the common language of the educated classes.
C) Song culture was a joyful melange of Han and pastoralist traditions, providing everyone with a sense of inclusion.
D) The mandate of heaven provided the Song a belief in their cultural uniqueness, centered on their divine ruler.