The Fund seeks to track the investment results of the ICE BofA BB US High Yield Constrained Index (the Underlying Index), which measures the performance of the BB, or equivalently rated, fixed-rate, U.S. dollardenominated, corporate bond market. The Underlying Index is a subset of the ICE BofA US High Yield Constrained Index that is market capitalizationweighted with a 2% cap on any one issuer and a pro rata distribution of any excess weight across the remaining issuers in the Underlying Index. the Fund will invest at least 90% of its assets in fixed income securities of the types included in the Underlying Index that BFA believes will help the Fund track the Underlying Index. The Fund will invest no more than 10% of its assets in futures, options and swaps contracts.