美国至7月28日6个月国债竞拍-得标利率配置百分比 51.81%，前值81.6%。

Group 1 - The core point of the article indicates that the bid-to-cover ratio for the 6-month U.S. Treasury bill auction as of July 28 was 51.81%, a significant decrease from the previous value of 81.6% [1]