Which standard library is used to access a file stored on a website?

The correct choice is relevant to the task of accessing files stored on a website, as it specifically provides functionalities for handling URLs. The library in question, urllib, is a module in Python that allows for retrieving data from web pages and handling URLs effectively. It is designed to work seamlessly with internet protocols, enabling operations such as opening and reading files from web resources.

When using urllib, you can easily make HTTP requests, handle different data types, and deal with URL-related tasks, such as encoding or parsing. This makes it an essential tool for tasks that involve web-based file access.

In contrast, os is primarily used for operating system functionalities, such as file and directory manipulation on the local file system, and it does not inherently support web protocols. pdb is a debugger for Python programs, which does not pertain to file access from websites, while sys provides access to system-specific parameters and functions, also unrelated to networking or web-based file operations. Therefore, urllib is the most suitable library for accessing files stored on a website.