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Why companies appear in several stock exchanges?
The case you are looking at is rather special, because the Chinese government for the longest time did not allow foreigners to invest in Chinese stocks. The ADRs explained in @DStanley's answer are a way around that restriction; recently there are some limited official ways,  In general, it is perfectly normal for a stock to appear on different exchanges, in different currencies, and it's all the "real" stock. Because remember: a stock exchange is really nothing more than a fancy place for people to buy and sell stocks. There is absolutely no reason why a specific stock should only be traded in one place. Companies that have decided to be publically tradeable generally want to be traded in as many exchanges as possible, because it makes the stock more liquid, which helps their shareholders. Individual exchanges have different requirements for a stock to be listed for trading there, some may even do it without the company's explicit approval.