Which of the following expansion buses is most commonly used for devices such as sound cards, modems, and NICs?

The most commonly used expansion bus for devices such as sound cards, modems, and network interface cards (NICs) is the PCI bus. The Peripheral Component Interconnect (PCI) bus was widely adopted in computer systems and serves as an interface between the motherboard and various expansion cards. Its architecture allows for faster data transfer rates compared to older standards like ISA, making it suitable for devices that require efficient performance.

PCI supports a plug-and-play feature that allows the operating system to automatically configure devices when they are installed, thereby simplifying the installation process. Though newer standards like PCIe provide even greater speeds and bandwidth, PCI remains a prevalent choice for many legacy and current peripherals where extreme performance is not critical.

Devices like sound cards or NICs benefit from PCI due to its adequate speed for data transfer without requiring the advanced features of PCIe. In contrast, AGP was specifically designed for graphics cards, ISA is an older bus standard with lower performance that has largely been phased out, and PCIe, while offering superior performance, is typically reserved for high-speed devices.