Explanation:

The correct answer is (a) Portions of the operating system are copied from disk into memory. This is a fundamental step in the booting process. When a PC starts, the Basic Input/Output System (BIOS) or Unified Extensible Firmware Interface (UEFI) performs initial hardware checks. It then loads a small program called the bootloader, which in turn loads the essential parts of the operating system kernel and other critical components from the hard disk (or other storage device) into the computer's Random Access Memory (RAM). This allows the operating system to begin execution and take control of the system. (b) Portions of the operating system are copied from memory onto disk: This describes the process of saving data from RAM to a storage device, which is the opposite of what happens during booting. This occurs during operations like saving files or hibernation. (c) Portions of the operating system are compiled: Compilation is the process of translating source code into machine code, typically performed by software developers before the operating system is distributed. It is not an event that occurs every time a PC boots up. (d) Portions of the operating system are emulated: Emulation involves one system imitating another. While virtual machines use emulation, it is not the standard process for booting a physical PC's native operating system. (e) The PC gets switched off: This is the opposite of booting up. Booting is the process of starting the PC, not shutting it down.