To solve this question, the user needs to know about the different types of web applications that exist and their characteristics.

The correct answer is:

C. Web services

Explanation:

Web services are a new breed of web application that allows different systems to communicate with each other over the internet. They are a collection of standards-based technologies that provide a way for applications to exchange information, regardless of the platform or programming language used to build them. Web services are designed for machine-to-machine communication, enabling different systems to exchange data and functionality without the need for human intervention.

Option A, Web controls, refers to user interface elements that are used to interact with web applications. They include buttons, text boxes, drop-down lists, and other interactive elements that allow users to interact with web pages.

Option B, Web contents, refers to the information and media that is displayed on web pages. This includes text, images, videos, and other multimedia elements that are used to convey information to users.

Option D, Web pages, refers to the documents that are served by web servers and displayed in web browsers. Web pages can be static or dynamic, and can contain a variety of content, including text, images, videos, and interactive elements.

Therefore, the correct answer is C, Web services.