老师： 您好！
您看以下我的理解正确吗？ 如有理解错误的地方，麻烦指出来，谢谢！
1)It's a pity that he should refuse to accept the offer.
已经拒绝了。动作已经发生了。
2)It's a pity that he should have refused to accept the offer.
已经拒绝了。动作已经发生了。 （should have refused 现在不常用了，以前流行用）
It's a pity that he refuses to accept the offer.
这是错句。
3) It is regrettable that they should leave.
已经离开了。动作已经发生了。
4) It is regrettable that they should have left.
已经离开了。动作已经发生了。
It is regrettable that they leave.
这是错句。
另外： 补充2句：
It's a pity that he refused to accept the offer.
用refused - 也是正确的。
It is regrettable that they left.
用left - 也是正确的。
以上，有should ,表示居然，竟然等感情之意，没有should, 则没有感情之意。
麻烦老师逐一仔细看一下，指出我错误的地方！ 非常感谢！