Which device connects SAS initiators, expanders, and targets?

A.
backplane

B.
expander

C.
initiator

D.
target

Explanation:
The components known as Serial Attached SCSI Expanders (SAS Expanders) facilitate communication
between large numbers of SAS devices. Expanders contain two or more external expander-ports. Each
expander device contains at least one SAS Management Protocol target port for management and may contain
SAS devices itself. For example, an expander may include a Serial SCSI Protocol target port for access to a
peripheral device. An expander is not necessary to interface a SAS initiator and target but allows a single
initiator to communicate with more SAS/SATA targets. A useful analogy: one can regard an expander as akin to
a network switch in a network, which connects multiple systems using a single switch port.
https://en.wikipedia.org/wiki/Serial_Attached_SCSI#SAS_expanders