Why was the porcelain of the Song era of such high quality?

Several of these regional ceramic wares were so valued during their day that they were used as tribute and yearly taxes to the imperial court. In terms of technical expertise, inventiveness, and aesthetic perfection of glaze and shape, the Song period stands unrivaled for the quality of its ceramic ware.

Explanation:

the fact that could also be added to column b is that during world war ii, specifically between the years 1941 and 1945, japan expanded its territory towards the indonesian territory in what was known later as part of the "pacific war". in that time, japan could conquer the philipines, singapore,   borneo, central java, malang, cebu, sumatra and various other islands of the area, therefore expanding its territory for a brief period of time.