Explanation: SITOR (SImplex Teletype Over Radio) in ARQ (Automatic Repeat reQuest) mode is designed for reliable, two-way communication. In ARQ mode, the "information sending station" transmits data in blocks, typically three characters at a time. After sending a block, it pauses and waits for an acknowledgment from the "information receiving station." If the receiving station successfully decodes the block, it sends a positive acknowledgment (ACK). If it detects an error, it sends a negative acknowledgment (NACK), prompting the sending station to re-transmit that specific block. This block-based, acknowledge/retransmit mechanism ensures data integrity. Options A and C describe characteristics more aligned with SITOR's FEC (Forward Error Correction) or broadcast mode (SITOR-B), where characters are often transmitted redundantly (twice) or interleaved to combat fading, without requiring an acknowledgment. Option D is incorrect because NAVTEX is a one-way broadcast system for maritime safety information, not an interactive system that allows user stations to request specific repeats via SITOR.