Besides isolationism, another reason why china limited trade was because

a. europeans valued their goods at much higher than their actual worth.
b. the chinese wanted to prevent their ports from being polluted by foreign ships.
c. the chinese were only interested in the gold and silver europeans had to trade.
d. europeans continued to bring their missionaries to convert the chinese

"Europeans valued their goods at much higher than their actual worth." even if that was the case, the limitation was set by the Chinese

"b.the Chinese wanted to prevent their ports from being polluted by foreign ships." this is not really true and also, a lot of the commerce wasn't made by sea.

"d.Europeans continued to bring their missionaries to convert the Chinese" also not the case back then.

The fact is that the Chinese had only one interest, precious metals. And the only answer that represents that is:

"c.the Chinese were only interested in the gold and silver Europeans had to trade."

payments were made after the 1940s.

in the 1980s, a commission held investigations and made recommendations.