Answer:
advanced art is probably the best pick here.
Step-by-step explanation:
First off, goo-gle post-classical China. It's the era of late Han dynasty to Song dynasty when the Tartars from the North haven't invaded into central China. During this era, China was undoubtedly the most powerful country in terms of technology development and population. Foreign trade was prosperous.
Japan was in a good relationship with China from time to time. The Kentoshi(commissions) they sent to learn from Tang(the 'To' in 'Kentoshi') dynasty significantly speeded up their technology.
Bodhidarma did spread buddhism in China around the fifth century, and Zen buddhism, apart from the Buddhism in India, is founded then. However, I guess the gun powder and population growth has nothing to do with this.