问题补充：
I am writing this letter to express my regret that I can’t go to the Great Wall with you next weekend. It’s really pity. I feel sorry for them and want you to know that happened.
Yesterday, my father, worked in the United States now, informed me that he would be back to home tomorrow. I was very happy when I heard the news. Father and I had not seen each other for two years, but I am really looking forward to this meeting.
I sincere hope that you can be able to think in my position and accept my apology. I would appreciate your allowing me to make another dates to go to the Great Wall.
Once again, I am sorry for any inconvenience I have caused.really 和pity 之间加a
答案：
(答案→)really 和pity 之间加a
解析：本文是一封道歉信：我很遗憾和抱歉不能在下周末和你一起去长城玩，因为我现在在美国工作的爸爸通知我他明天回家，因为两年没见，所以很期待这次见面。希望你谅解并接受我的道歉，我们可否改日再一起去长城。再次为带来的不便表示歉意。
【小题1】pity做可数名词是：可惜的事。It’s a pity 意为：这事很可惜。
【小题2】本句应该理解为：我为此感到很抱歉。代词应该指代前面的这件事要用it 。
【小题3】 know 后是宾语从句，在宾语从句中that 只起连接作用，而what 要做句子成分，在这里作主语用what。
【小题4】my father 后面还有逗号，所以用非谓语形式作定语，worked表示和主语是逻辑上的被动关系，而work 与主语是逻辑上的主谓关系，应该用working 。
【小题5】home是副词，副词前不用介词。所以去掉前面的to 。
【小题6】通读全文和本句的for two years 提示本句应该用现在完成时，主语是复数Father and I ，所以谓语要用助动词have 以保持主谓一致。
【小题7】通过分析前后关系可知，这里是因果关系而不是转折关系。So 意为“所以”。
【小题8】 sincerely 副词修饰动词 hope.。英语中习惯用形容词修饰名词，副词修饰动词。
【小题9】can 和 be able to 是一个意思，不能同时用。用will 表将来。
【小题10】make another date 意为：改日。another 意为：另一个，后面要用单数可数名词。
