Which transmission mode is supported by both HDLC and SDLC?

A.
Asynchronous Balanced Mode (ABM)

B.
Asynchronous Response Mode (ARM)

C.
Normal Balanced Mode (NBM)

D.
Normal Response Mode (NRM)

Explanation:
Answer D is correct; both HDLC and SDLC support Normal Response Mode (NRM), where secondary nodes can transmit when given permission by the primary.

Incorrect Answers and Explanations: A, B, and C: Answers A, B, and C are incorrect. HDLC supports Asynchronous Balanced Mode (ABM) and Asynchronous Response Mode (ARM), while SDLC does not. There is no such mode as Normal Balanced Mode (NBM).