string(311) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E7%9B%88%E4%BA%8F%E5%B9%B3%E8%A1%A1%E7%82%B9%E7%9A%84%E8%AE%A1%E7%AE%97%E5%85%AC%E5%BC%8F%E6%98%AF%E4%BB%80%E4%B9%88%E6%A0%B7%E7%9A%84%E5%91%A2 => Failed to connect to 101.91.112.32 port 38221: Connection refused"
盈亏平衡点的计算公式是什么样的呢
