为什么美元涨？这个问题涉及到货币价值的变化，通常受到多种因素的影响。以下是对这个问题的解析以及英文翻译对照：

首先，美元的价值通常受到全球经济形势的影响。当全球经济稳定、经济增长强劲时，投资者会寻求将资金投入高收益的资产，如股票和债券等。这种情况下，美元可能会上涨，因为投资者将资金投入其他国家的资产时，需要使用美元作为交易货币。英文翻译为：Firstly, the value of the US dollar is often influenced by the global economic situation. When the global economy is stable and economic growth is strong, investors may seek to invest their funds in high-yielding assets such as stocks and bonds. In this case, the US dollar may rise because investors need to use the US dollar as a transaction currency when investing funds in other countries' assets.

其次，美元汇率还受到美国国内经济和货币政策的影响。当美国经济表现良好、利率较高时，投资者可能会将资金投入美国市场，从而推高美元汇率。此外，美国政府和央行的货币政策也可能影响美元汇率。例如，美联储可能会采取量化宽松政策来刺激经济，这将导致美元供应增加，从而降低美元汇率。英文翻译为：Secondly, the exchange rate of the US dollar is also influenced by the domestic economy and monetary policy of the United States. When the US economy performs well and interest rates are high, investors may invest their funds in the US market, thereby driving up the exchange rate of the US dollar. In addition, the monetary policy of the US government and the Federal Reserve may also affect the exchange rate of the US dollar. For example, the Federal Reserve may adopt quantitative easing policies to stimulate the economy, which will increase the supply of US dollars and thereby lower the exchange rate of the US dollar.

综上所述，美元涨受到全球经济形势、美国国内经济和货币政策等多种因素的影响。这些因素共同作用，导致了美元汇率的波动。英文翻译为：In summary, the rise of the US dollar is influenced by various factors including the global economic situation, the domestic economy and monetary policy of the United States. These factors act together to drive the fluctuations of the exchange rate of the US dollar.