To which of the following components does a technician mount a 1U server in a rack?

Rail kits consist of sliding or fixed rails that attach to the front and rear vertical posts of a rack enclosure and directly support the chassis weight of a 1U server. They are purpose-built for rack-mountable server form factors and allow the server to slide in and out of the rack without full removal for easier servicing.

A shelf is a flat platform used to place non-rack-mountable equipment that lacks integrated ear brackets inside a rack, not for 1U servers designed to use rail kits.

A KVM switch is a peripheral sharing device that allows one keyboard, monitor, and mouse to control multiple servers and is not a mounting component.

A block-off (blank) panel is a filler plate installed in empty rack unit slots to maintain proper airflow and does not provide structural mounting support for servers.