Explanation: Fiber-optic gyro compasses operate based on the Sagnac effect. Light is sent in opposite directions through a coiled optical fiber. If the coil is rotating, the light traveling with the rotation has a slightly longer path (or takes longer) than the light traveling against the rotation, creating a measurable phase difference. This phase difference is directly proportional to the rotation rate. To determine true north, three fiber-optic coils are used, oriented orthogonally to measure angular rotation about all three axes (roll, pitch, and yaw). This allows the system to detect the Earth's rotation vector relative to its own frame. A dual-axis electronic level sensor provides critical information about the compass's tilt (pitch and roll) relative to the horizontal plane. By knowing the local latitude and the system's orientation relative to gravity, the gyrocompass can resolve the component of the Earth's rotation that defines the direction of true north. Options A, B, and C are incorrect because they either specify an insufficient number of coils for 3-axis sensing or incorrectly emphasize accelerometers as the primary rotation detection mechanism for a fiber-optic gyrocompass. Accelerometers measure linear acceleration, not angular rotation, and while they can be part of an Inertial Measurement Unit (IMU), they don't replace the core fiber-optic rotation sensors.