自动索引

例句：

1. 1. The search engine automatically indexes the web content for us.
   搜索引擎自动为我们索引网页内容。
2. 2. The index system is designed to automatically track and categorize data.
   索引系统旨在自动跟踪和分类数据。
3. 3. The library has a large collection of books that are indexed by subject.
   图书馆拥有大量按主题索引的书籍。