closure of a set

例句：

1. 1.The door was closed tightly behind him.
   门在他身后紧紧地关上了。
2. 2. The factory has been closed for repairs.
   工厂因维修而关闭。
3. 3.The book's closure is a surprise to many readers.
   这本书的结尾让许多读者感到惊讶。