求翻译：第一，美元停止兑换黄金。 1971年7月第七次美元危机爆发，尼克松政府于8月15日宣布实行“新经济政策”，停止履行外国政府或中央银行可用美元向美国兑换黄金的义务。这意味着美元与黄金脱钩，支撑国际货币制度的两大支柱有一根已倒塌。是什么意思？

First, the dollar stopped gold convertibility. Seventh dollar crisis in July 1971, the Nixon administration announced the introduction of a "new economic policy" on August 15, ceased to perform the obligations of foreign governments or central banks available to the United States for $ gold converti