could have done 表示“(过去)可能已经做过”,表示对过去情况的推测,但多用于否定句或疑问句中。该短语还可表示虚拟,表示“本可能做某事,但实际上未做”。
could have done的否定形式是could not have done,表示“不可能做过”。
Frederick William I, the King of Prussia,could never have imagined that his greatest gift to the Russian people would have such an amazing history.
普鲁士国王腓特列▪威廉一世绝不可能想到他送给俄罗斯人名的厚礼会有这样一段令人惊讶的历史。