Passage: Customs gold units (關金圓, pinyin: guānjīnyuán) were issued by the Central Bank of China to facilitate payment of duties on imported goods. Unlike the national currency which suffered from hyperinflation, the CGUs were pegged to the U.S. dollar at 1 CGU = US$0.40.

Question: What is the name of the country where guānjīnyuán was a currency?
China