Explanation: During daytime hours, LORAN (Long Range Navigation) systems primarily relied on ground wave propagation for accurate position determination. Ground waves travel along the Earth's surface and are attenuated by the Earth's conductivity and diffraction. For LORAN-C, which operated in the 90-110 kHz range, the maximum reliable range for ground wave reception suitable for determining lines of position (LOPs) was approximately 600-800 nautical miles. Therefore, 700 miles is a good approximation. While skywaves can travel much further, especially at night (as mentioned in option B), they are highly variable and introduce significant errors for precise time-difference measurements required for LORAN LOPs. The question specifically asks about daytime distance, where skywave propagation is less reliable and accurate at these frequencies due to absorption in the ionosphere's D-layer. Options C and D are too high for reliable daytime groundwave propagation.