Explanation: Log entries for amateur radio, especially concerning international events like the silent period, must use a universal time standard to ensure consistency and avoid confusion across different time zones. **Why B is correct:** * **Greenwich Mean Time (GMT)**, often used interchangeably with Coordinated Universal Time (UTC) or "Zulu Time," serves as the international standard for timekeeping in radio communications. This prevents discrepancies that would arise from using local times, which vary globally. * The **24-hour system** eliminates ambiguity inherent in the 12-hour (AM/PM) system. For example, 1 PM could be misread as 01:00 or 13:00 if not specified. Using 24-hour format (e.g., 13:00) provides precise, unambiguous time references, critical for regulatory compliance and synchronized international operations like observing silent periods. **Why others are incorrect:** * **A and C (Zulu time according to the 12-hour system)** are incorrect because, while Zulu time (UTC/GMT) is the correct standard, the 12-hour system introduces ambiguity (AM/PM), which is undesirable for official log entries. * **D (None of the above)** is incorrect because option B correctly identifies the universally accepted time standard and format for radio logs.