Which of the following keystrokes or characters is sent as part of ARQ communications to end the radio link?

Correct Answer: Option C — BRK+

In SITOR ARQ operations, 'BRK+' is the standard command used by the ship station to request a break in the radio link or to signal the coast station to stop the current transmission. It is a control command used to manage the flow of the session before final termination of the connection.