string(328) "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%E6%95%B0%E9%87%8F%E5%8F%98%E5%8C%96%E7%9A%84%E5%8E%9F%E5%9B%A0%E6%9C%89%E5%93%AA%E4%BA%9B => Failed to connect to 61.171.74.35 port 38027: Connection refused"
中国持有美国国债数量变化的原因有哪些
