string(265) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E4%B8%AD%E5%9B%BD%E6%8C%81%E6%9C%89%E7%BE%8E%E5%9B%BD%E5%9B%BD%E5%80%BA%E5%A4%9A%E5%B0%91%E4%BA%BF => Failed to connect to 14.18.117.71 port 38041: Connection refused"
中国持有美国国债多少亿
