Return-from-trap instruction returns into the calling user program while simultaneously reducing the privilege level back to Select one: a. User mode b. Kernel mode c. OS mode d. CPU mode

A. user mode

Explanation:

A computer system is a machine that is run by a series of programs that connect the virtual parts (software) to the hardware or electronic parts. The kernel is a computer program that connects the software and hardware of a computer system.

The kernel-mode has several privileges like I/O, interrupts and traps, etc. This mode is tapped by root or administrators to utilize these privileges. Unlike the kernel mode, the user-mode does not have these functions, so a return from the trap instruction (kernel) reduces the privileges back to the user mode.