Answer: Option B. -> Basic Input Output system

Answer: Option A. -> power switch of computer is turned ON

Answer: Option B. -> Ctrl – Alt – Delete

Answer: Option C. -> Disk Operating System

Answer: Option E. -> DOS
An operating system (OS) is a software that manages a computer's hardware resources and provides common services for computer programs. An OS can be categorized based on its functionality and structure. One way to categorize OS is based on the number of users it can support simultaneously. Based on this, an OS can be classified as a single-user operating system or a multi-user operating system.
A single-user operating system is an OS that supports only one user at a time. In this type of OS, the computer can be used by only one user, and all system resources are dedicated to that user. Here are some of the features of a single-user operating system:

• The user has complete control over the system.
• The user can install and run any application.
• The user can modify system settings.
• There is no need for security measures to protect data from other users.

DOS, which stands for Disk Operating System, is an example of a single-user operating system. It was popular in the 1980s and 1990s and was used on IBM-compatible personal computers. Here are some of the reasons why DOS is a single-user operating system:

• DOS supports only one user at a time. When the computer is turned on, it boots directly to the DOS prompt, which is a command-line interface.
• DOS does not have built-in security features to protect data from other users. All files and directories are accessible to the user who is currently logged in.
• DOS does not have multi-tasking capabilities, which means that only one program can run at a time.

In conclusion, the correct answer to the question is E. DOS.

Answer: Option C. -> DOS 6.22

Answer: Option A. -> multitask

Answer: Option D. -> All of the above

Answer: Option A. -> two or more central processing units within a computer system

Answer: Option C. -> multi-user
Multi-user is the term used to describe a system in which multiple users can access the same computer system at the same time. This system is commonly found in corporate networks, educational institutions, and other large organizations. The main advantage of this system is that it allows multiple users to access the same resources, such as files and applications, without having to manage and maintain separate systems for each user.

Definition:
Multi-user: Multi-user is a system in which multiple users can access the same computer system at the same time.

Explanation:
Multi-user is different from the other options in that it does not involve the execution of multiple programs by a single CPU. It is simply a system that allows multiple users to access the same computer system at the same time. The main advantage of this system is that it allows multiple users to access the same resources, such as files and applications, without having to manage and maintain separate systems for each user.

Multi-processing and Time Sharing:
Multi-processing and time sharing are two related concepts. Multi-processing is the simultaneous execution of multiple programs by a single CPU. Time sharing is a form of multi-processing in which multiple users can simultaneously access the same computer system. Time sharing is commonly used in corporate networks, educational institutions, and other large organizations.

Multi-programming:
Multi-programming is the execution of multiple programs by a single CPU. It is a form of multi-processing in which multiple programs are loaded into the CPU's memory at the same time. The CPU then switches between the programs, executing each one in turn. The advantage of multi-programming is that it allows multiple programs to be executed simultaneously, thus increasing overall system performance.

Conclusion:
From the above explanations, it is evident that the correct answer is option C - Multi-user. Multi-user is the term used to describe a system in which multiple users can access the same computer system at the same time. It is different from multi-processing and time sharing in that it does not involve the execution of multiple programs by a single CPU. Additionally, it is different from multi-programming in that it does not involve the loading of multiple programs into the CPU's memory at the same time.