Answer: All were culturally influenced by China
Explanation:
In the period 600 C.E. to 1450 C.E. States in japan, Korea, and Vietnam were culturally influenced by China.
An example is regarding Buddhism which was spread to Korea, Japan and Vietnam from China. Japan's music was influenced by China. New music styles were being introduced and also, new musical instruments were imported from China. During Buddhist ceremonies, musical instruments such as gongs, rattles ans bells were brought from China which later became part of their history.
The writing system in Korea coupled with their architecture, musical instruments, religion, political system were influenced by China. Also, the Silla military made use of Chinese belief systems like Buddhism, and Confucianism).
Architecture, government styles, language and art forms were also used by Japanese and these were borrowed from the Chinese. During this periods, when writing, the Japanese nobles made use of the Chinese language.