Final answer:
The cultural practice of the people in Jinhan, Korea that suggests they were in contact with Japan is language.
Step-by-step explanation:
The cultural practice of the people in Jinhan, Korea that suggests they were in contact with Japan is language. One of the major cultural exchanges between ancient Korea and Japan was the introduction of written language from China, which influenced both countries. Korean society adopted Chinese script for record-keeping and communication, and this practice would have likely been shared with Japan during their interactions.