ETF（Exchange Traded Fund）是一种基金投资工具，它可以在证券交易所上市交易，类似于股票。ETF的基本原理是通过购买一篮子的股票、债券或其他资产，来追踪特定的指数或行业。ETF的特点包括流动性强、投资门槛低、成本较低等。

ETF的流动性强是其最大的优势之一。由于ETF可以在证券交易所上市交易，投资者可以随时买入或卖出，不受基金份额的限制。相比于传统的共同基金，ETF更加便捷灵活，投资者可以根据市场行情随时进行交易。

ETF的投资门槛相对较低。购买ETF只需要购买一股即可，而传统的共同基金则需要购买整数份额。这使得小额投资者也能够参与到ETF的投资中来，享受到多样化投资的机会。

ETF的管理费用相对较低。由于ETF是 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 passively managed，即 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