Answer:
The three traditions that coexisted in China from ancient times till today are: Buddhism (which was the religion that was assimilated into China), Daoism and later on Confucianism. Buddhism was brought around to China by migrating monks from India around the 6th century BC and these three traditions were able to coexist because of two reasons: One, China never had a strong religion to begin with, and two, because these three traditions began to share elements, especially the language. With time, Buddhism was not only accepted, but assimilated to the point that it became a permanent religion, and one of the strongest, in China.
Step-by-step explanation:
It is important to first comprehend that China has never had a truly strong religious tradition. From its formation as a nation during the Han dynasty onwards, China has not had one overpowering religion like other nations.
In the case of Buddhism, which migrated into China from India around the sixth century BC, brought in by migrating monks, it was assimilated into Chinese culture both because of this lack of a strong religion, and also because the principles proposed and practiced by Buddhism coincided a lot with the only religious tradition present in China up until that century: Daoism. These two religions were able to coexist and not clash against one another because Buddhism borrowed several elements from Daoism and integrated them.
Later on, when Confucianism was born as a tradition in China, the two traditions also shared a lot of the beliefs, plus by this time Buddhism had already been assimilated not only by the Chinese people but also by the emperors themselves. So when Confucianism came along, they just easily shared elements and thus no confrontation became necessary.