A technician needs to install more add-on cards than there are available expansion slots. Which of the following would allow the technician to accomplish this?

A backplane is a passive or active board used to connect hot-swappable drives or blade modules to a system, not a device that increases the number of PCIe expansion slots.

A CPU daughterboard is an add-on board used to install additional or upgraded processors on supported platforms, not a mechanism for gaining more expansion card slots.

A riser card is a small PCB that plugs into one of the motherboard's existing PCIe or legacy expansion slots and extends it into one or more additional slots, typically oriented perpendicular to the board to fit within constrained server chassis heights. This allows more add-on cards to be installed than the motherboard's native slot count would otherwise permit. Riser cards are a standard solution in rack-mount servers where space and slot availability are limited.

An array controller (RAID controller) manages disk arrays for redundancy and performance purposes and does not provide any additional expansion slots to the system.