Explanation: MF-HF Digital Selective Calling (DSC) utilizes time diversity to enhance reception reliability, particularly crucial given the often-unpredictable propagation on medium and high frequencies. For MF-HF-DSC, each character within a message is transmitted twice. The second transmission of a specific character occurs 400 milliseconds after its initial transmission. This 400ms interval allows for significant time separation between the identical data, increasing the likelihood that at least one of the transmissions will be received correctly, even if the signal experiences a deep fade or interference due to multipath propagation. The receiver can then combine the information from both attempts, improving the overall decoding success rate. Options A, C, and D do not correspond to the specified time diversity interval for MF-HF-DSC signaling.