The correct answer is: B. Buddhist beliefs spread throughout China.
Emperor Wen's reunification of China during the Sui Dynasty helped create a more stable environment where Buddhism could spread and gain greater influence throughout the country. While the Sui Dynasty itself was relatively short-lived, its efforts in promoting Buddhism had lasting impacts on Chinese culture and religion.
Options A, C, and D are not accurate results of the reunification under Emperor Wen. The Han Dynasty did not return, Korea was not conquered during the Sui Dynasty's period, and the Sui Dynasty did not rule for centuries; it lasted only a few decades.