The correct answer is D: Radiation at low angles increases. The far-field elevation pattern of a vertically polarized antenna when mounted over seawater versus soil shows increased radiation at low angles. Seawater has much higher conductivity than soil, reducing ground losses and improving low-angle radiation. Seawater's high conductivity creates a better ground plane effect than soil. This reduces ground losses and improves the antenna's efficiency, particularly at low elevation angles. Low-angle radiation is important for long-distance communications because signals at shallow angles can travel farther via ionospheric skip. The improved ground plane from seawater enhances this low-angle radiation, making vertical antennas much more effective over seawater than over typical soil.