Explanation:

The correct option is (B) slots. Expansion slots, such as PCI, PCIe (Peripheral Component Interconnect Express), or AGP (Accelerated Graphics Port) slots, are physical connectors on the motherboard that allow users to add expansion cards. These cards, like graphics cards, sound cards, network cards, or storage controllers, enhance the computer's functionality and provide additional capabilities. Option (A) sockets are typically used for the CPU or RAM modules, allowing for component installation or upgrades, but 'slots' more specifically refers to adding *expansion cards*. Option (C) bytes are units of digital information, not physical components. Option (D) bays are physical enclosures within the computer case designed to hold storage drives (e.g., hard drives, SSDs, optical drives), not for adding functional expansion cards.