求if的虚拟语气用法,需要怎样注意时态的问题,

should(第一人称)和would(第二三人称)+动词原形 should(第一人称)和would(第二三人称)+have+过去分词 If I were you,I should take his advice.He said he would go if I went.If father hadn't sent me,I shouldn't...