Introduction:
An operating system is a software that manages computer hardware and software resources and provides common services for computer programs. It acts as an intermediary between the computer hardware and the user, allowing the user to interact with the computer and run various applications. There are several examples of operating systems available today. Let's discuss each option given and explain why the correct answer is option 'D', which states that all of the above options are examples of operating systems.

Explanation:

1. Windows:
- Windows is a widely used operating system developed by Microsoft.
- It is designed to run on personal computers, laptops, tablets, and servers.
- It provides a graphical user interface (GUI) that allows users to interact with the computer using windows, icons, menus, and pointers.
- Windows supports a wide range of software applications and hardware devices.
- It includes various features such as file management, multitasking, networking, and security.

2. Android:
- Android is an operating system primarily designed for mobile devices such as smartphones and tablets.
- It is developed by Google and is based on the Linux kernel.
- Android provides a customizable user interface and supports millions of applications available on the Google Play Store.
- It offers features like multi-touch gestures, notification system, and integration with Google services.
- Android is widely used in smartphones and has a large market share in the mobile operating system market.

3. DOS:
- DOS (Disk Operating System) is an operating system that was popular in the early days of personal computers.
- It was developed by Microsoft and used a command-line interface for interacting with the computer.
- DOS supported basic file management and ran on computers with limited hardware resources.
- While it is not widely used anymore, it played a significant role in the development of operating systems.

Conclusion:
All of the given options (Windows, Android, and DOS) are examples of operating systems. They are designed to manage computer hardware and software resources, provide user interfaces, and support various applications.