It may be too costly or impractical to replicate the targeted index completely. To synthesise it, the ETF provider usually enters into a transaction known as a total return swap with a bank.

完全复制目标指数也许太昂贵了或是不切实际的，为了达到混合的目的，ETF的供应商往往和银行进行一个被称为总收益互换的交易。

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The note consists of futures of contracts of seven agricultural commodities (soybeans, corn, wheat, cotton, soybean oil, coffee and sugar) and tracks the return of the Dow Jones-UBS Agriculture Total Return Sub-Index.

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You could, for example, buy the iPath Dow Jones-AIG Lead Total Return Sub-Index or PowerShares DWA Emerging Markets Technical Leaders.

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The iPath DJ-UBS Copper Total Return Sub-Index ETN ( JJC) is the most liquid of the exchange traded products that follow copper prices.

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