正解:B,D
Explanation
The data link layer is responsible for defining the format of data on the network and providing physical transmission of data. Devices that operate at this layer include switches and network interface cards (NICs).
Encapsulations that are used at this layer include frames, which are units of data that contain a header, payload, and trailer. Frames are used to identify the source and destination of data on the network and to perform error detection. References: CompTIA Network+ N10-008 Certification Study Guide, page 9; The Official CompTIA Network+ Student Guide (Exam N10-008), page 1-6.