string(260) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=2021%E7%89%88%E4%BA%8C%E7%BA%A7%E5%BB%BA%E9%80%A0%E5%B8%88%E6%95%99%E6%9D%90%E5%8F%98%E5%8C%96 => Failed to connect to 14.18.117.71 port 38220: Connection refused"
2021版二级建造师教材变化
