ー It's useless to regret what has been done. Don't make those mistakes again.
— I won't. That's a(n) _____.
名词词义的辨析
句意：—— 后悔已经做过的事情是没有用的，不要再犯那些错误了。—— 我不会了，这是一个承诺（我承诺）。本题考查名词词义辨析。选项A “订单，命令”；选项B “决定”；选项C “许诺”；选项D “承诺”。根据句意可知 “我发誓不再犯那些错误了”。
The train travelled _____ fast for us to see much outside the window.
考查too…to…的用法。句意：对我们来说，火车跑得太快了而无法看到很多窗外的景色。too…to…表示 “太……而不能……” 是固定搭配。
He promised _____ his old friend during his stay in Tianjin.
非谓语动词的用法
考查非谓语动词的用法。句意：他答应待在天津期间去看望他的老朋友。promise to do sth. 意为“承诺做某事”，故选选项D。
— Hi,Susan! What are you going to do during the summer holiday?
— I'm going to _____ cooking because I like eating delicious food.
句意：—— 你好，苏珊！暑假期间你打算做什么？—— 我打算从事烹饪，因为我喜欢吃美食。本题考查动词短语。clean up 打扫干净；put up 举起，张贴；take up 开始从事；make up 弥补。根据句意可知，选C选项。