2011年以来,美欧日等发达国家的主权债务危机越演越烈。美国标准普尔评级公司给美国的长期国债降级,欧元区一些成员的债务频频受到市场的质疑,希腊、西班牙、意大利的国债利息率不断上升,也遭到美国评级公司的降级。但与此同时,美欧日等国 Since 2011, the sovereign debt crisis in developed countries such as the United States, Europe and Japan has become increasingly fierce. Standard & Poor’s rating agency downgraded the long-term US government debt. Some members of the euro zone’s debt has been questioned by the market frequently. Interest rates on bonds of Greece, Spain and Italy have been rising, and their ratings have been downgraded by U.S. rating agencies. But at the same time, the United States, Europe and Japan and other countries