To solve this question, the user needs to have basic knowledge about operating systems and their functions.

Now, let's go through each option and explain why it is right or wrong:

A. System boot: This option is correct. One of the main functions of an operating system is to manage the boot process of a computer. When a computer is turned on, the operating system is responsible for loading and initializing the necessary components to start the system.

B. Running applications: This option is also correct. Another important function of an operating system is to manage and run applications on a computer. The operating system provides resources and services to enable applications to execute and interact with the hardware and other software components.

C. Both wrong: This option is incorrect. Both option A and option B are correct, as explained above.

D. Both correct: This option is correct. Both option A (System boot) and option B (Running applications) accurately describe functions performed by an operating system.

C. Both wrong: This option is incorrect. Both option A and option B are correct, so this option is not the correct answer.

D. Both correct: This option is incorrect. While both option A and option B are correct, this option does not accurately describe the functions of an operating system. It is more accurate to say that an operating system performs a wide range of functions, including system boot and running applications.

The Answer is: D