CPER tracks an index of copper futures. The index is reconstituted each month and selects two or three copper futures contracts. For the month of May, it currently holds Copper Sep14 and Copper Oct14 contracts.

USAG selects 14 futures contracts selected from soybeans, soybean meal, cotton, corn, canola, live cattle, soft red winter wheat, sugar, feeder cattle, hard red winter wheat, cocoa, lean hogs, soybean oil and coffee.

USMI follows a group of precious and industrial metals contracts, including primary aluminum, copper, nickel, zinc, lead, tin, platinum, silver, palladium and gold.

For more information on the ETF industry, visit our current affairs category.

Max Chen contributed to this article.