Which of the following keystrokes or characters is sent as part of ARQ communications to signal the end of communications with a land based TELEX terminal?

Correct Answer: Option B — KKKK

The sequence 'KKKK' is the internationally recognized signal in NBDP/SITOR communications to indicate the end of a telex message or the conclusion of a session with a land-based terminal. It signals the coast station to disconnect the radio link and generate the final message reference number and billing information.