虚拟语气中,什么时候用would have done,would do

虚拟语气中,什么时候用would have done,would do 虚拟语气的主句,什么时候用would do?什么时候用would have done? 虚拟语气中的would have done 与could have done结构 有什么 区别?什么时候用would什么 虚拟语气中对过去的虚拟主句否定是用would have not done or would not have done? 虚拟语气中had done与would have done,did与would do 的用法有何区别 虚拟语气would have done 的用法 would/could/must have done在虚拟语气中怎么用? 虚拟语气中的would/conld/should do/have done 与 did/had done有何区别 shall have done和would have done在虚拟语气句中是什么意思? 英语虚拟语气中sb should /would do(have done) 与主语人称的搭配有什么讲究吗 would have done 和would had done 分别用在什么句子中?请举例句说明（虚拟语气的用法） would have done和虚拟语气有关 would have sth是个什么语法概念?