Explanation:
A computer is an electronic device that can perform various tasks, such as storing, processing, and retrieving data. In order for a computer to function properly, it must have certain components and software.

Operating System:
An operating system is a software program that acts as an interface between the user and the computer. It manages the computer's hardware and software resources and provides common services for computer programs. Without an operating system, a computer cannot function.

Printer:
A printer is an output device that is used to produce a hard copy of the documents or files stored on the computer. Although a printer is not a mandatory component of a computer, it is often used to produce hard copies of important documents or files.

Word Processing Software:
Word processing software is a type of application software used to create, edit, and format text documents. While it is not mandatory for a computer to have word processing software, it is often used by individuals and businesses to create and edit documents.

Virus Checking Program:
A virus checking program is a software program that is used to detect and remove viruses, malware, and other malicious software from a computer. While it is important to have a virus checking program installed on a computer, it is not a mandatory component.

Conclusion:
In conclusion, a computer must have an operating system to function properly. While other components and software, such as a printer, word processing software, and virus checking program, are often used, they are not mandatory for a computer to function.

B