we know nothing about the man over there except____he is a American

昨天晚上回答得有些匆忙,现在纠正一下.这里的except是介词,"除了...之外",that作为连接词引导宾语从句.并不是只有动词可以接宾语从句,介词也可以,像I have no idea of what they are talking about. that不能省略,except后边通常接的是名次或代词,但是如果接的是名词性从句（这里是宾语从句）,连接词就不能省略.看以下几个句子：
1.The restaurant is open every day except Monday. 这家饭店除星期一外, 每天都营业. 2.Everyone except me got an invitation. 除了我以外, 所有人都收到了请柬.
3.I understand everything except why she killed him. 我一切都明白, 只是不理解她为什麽把他杀死了.
4.She remembered nothing (about him) except that his hair was black. 她（对他）什麽都不记得, 只记得他的头发是黑的.
问一下,你知道except, except for , besides, except that的区别不?