Which of the following is used when interconnecting FC switches?

An HBA (Host Bus Adapter) is used to connect a server (host) to a Fibre Channel switch or storage array, not to interconnect switches.

CAN (Controller Area Network) is a message-based protocol used in automotive and industrial automation, not for interconnecting Fibre Channel switches.

An Inter-Switch Link (ISL) is a physical or logical link between two Fibre Channel switches, allowing them to communicate and form a single, larger fabric. This enables devices connected to different switches within the fabric to communicate with each other.

Trunking, while a general networking concept, is not the specific term used for the logical connection between Fibre Channel switches; ISL is the precise Fibre Channel term.