Final answer:
XML is used within a web page to describe and transfer data between web service applications. It effectively encodes documents in a human-readable and machine-readable format for data exchange across services.
Step-by-step explanation:
The correct answer to the question is b) XML.
XML (Extensible Markup Language) is a markup language that is used to encode documents in a format that is both human-readable and machine-readable. It is specifically designed to store and transport data, making it ideal for describing and transferring data between web service applications. On the other hand, JSON (JavaScript Object Notation) is another data interchange format that is often used for this purpose. While HTML (HyperText Markup Language) is used for creating web pages and CSS (Cascading Style Sheets) is used for styling, they are not primarily used for describing and transferring data between web services.