a page has been turned的用法和样例：
- Flicking through the journal, Shanta came to a page that had been turned down.
- After a page has been updated, a read operation on the snapshot still accesses the original page, which is now stored in a sparse file.
- The number of times visitors click on a hyperlink (or advertisement) on a page, as a percentage of the number of times the page has been displayed.
- The corner of the page has been stuck down.