Which of the following indexes web pages and scans them to find a requested topic?

The search engine is the correct choice because it is specifically designed to index web pages and scan their content to locate information based on a user's query. When a user enters a search term, the search engine retrieves and displays relevant web pages that contain information related to that topic. This process involves crawling the web, indexing the content, and using algorithms to determine the relevance of each page based on the query.

In contrast, a general database refers to a structured collection of data that can be searched but does not crawl the web for content. A bookmark is a saved link to a specific web page for personal reference and does not involve searching or indexing at all. A URL, or uniform resource locator, is simply the address of a web page and does not perform any indexing or scanning functions. Thus, the capability of a search engine to efficiently gather and present information from across the internet makes it the appropriate choice for this question.