Task: Question Generation
Input (English): One of the more notable applications of printing technology was the chao, the paper money of the Yuan. Chao were made from the bark of mulberry trees. The Yuan government used woodblocks to print paper money, but switched to bronze plates in 1275. The Mongols experimented with establishing the Chinese-style paper monetary system in Mongol-controlled territories outside of China. The Yuan minister Bolad was sent to Iran, where he explained Yuan paper money to the Il-khanate court of Gaykhatu. The Il-khanate government issued paper money in 1294, but public distrust of the exotic new currency doomed the experiment.
Output (English): What were chao made out of?