改错：someone in the office had made a mistake,and the firm ((regretted to have casused))

题目

改错：someone in the office had made a mistake,and the firm ((regretted to have casused))
改错题：
someone in the office had made a mistake,and the firm ((regretted to have casused)) the customer inconvenient.
为什么括号里的错了,

答案

涉及到regret的用法：
regret doing sth.对某事感到后悔遗憾（已经发生的事）
regret to do sth.为要做的是感到后悔（动作未发生）
regret to have done将来完成时
regret having done:为做过的事感到后悔,抱歉
 
 
综上可见动作已经发生,且发生在过去,应与第四种情况吻合,故错误.
应改成regretted having accused.