Which of the following devices functions mainly at the data link layer of the OSI...

An SFP (Small Form-factor Pluggable) transceiver is a modular device that provides the interface between fiber-optic or copper cabling and the networking equipment (e.g., switch or router). It operates primarily at Layer 2 (Data Link), converting optical or electrical signals into frames usable by the network device.

A. SC is a fiber connector type, not the transceiver.

B. DAC (Direct Attach Copper) is a passive copper cable assembly with fixed transceivers, not a general-purpose module.

D. Twinaxial cable is a copper medium, not an interface device.

References (CompTIA Network+ N10-009):

Domain: Networking Concepts — Transceivers (SFP, GBIC, QSFP), fiber connectivity, OSI model mapping.