Which Statement Best Summarizes the Religious History of Southeast Asia

Which statement best summarizes the religious history of Southeast Asia?

A) Once predominantly Buddhist, the mainland is now mostly Muslim.
B) After long experience with Catholicism, the region's people are now mostly Protestant.
C) Many early Southeast Asian kingdoms switched back and forth between Hinduism and Buddhism as their principal religion.
D) Following a long history of Buddhism, the region is now primarily Confucian.