美国隔夜回购利率下行，逼近4%，美联储此前宣布国债购买计划。

Group 1 - The core point of the article is that overnight repurchase rates in the U.S. have declined, approaching 4%, following the Federal Reserve's announcement of a government bond purchasing program [1] Group 2 - The decline in overnight repurchase rates indicates a potential easing of liquidity conditions in the financial markets [1] - The Federal Reserve's bond purchasing plan may influence market dynamics and investor sentiment [1]