Which markup language is designed for documents that include structured information?

The correct choice is XML, as it is specifically designed for storing and transporting structured information in a way that is both machine-readable and human-readable. XML (eXtensible Markup Language) allows developers to define custom tags and the structure of data, making it versatile for a wide range of applications where data needs to be organized hierarchically. This capability to define the data structure makes XML particularly well-suited for scenarios where information needs to be shared across different systems or platforms, and where the structure of that information is important for understanding and processing the data correctly.

In contrast, HTML (Hypertext Markup Language) is primarily focused on the presentation of web pages and does not emphasize data structure in the way XML does. JSON (JavaScript Object Notation) is often used for data interchange, particularly in web development, but it is not as flexible in terms of defining complex structures as XML can be. CSV (Comma-Separated Values) is a simple format for tabular data and does not provide the capability for nested structures and metadata that XML does. Thus, XML stands out as the appropriate choice for documents containing structured information.