Explanation: The STC (Sensitivity Time Control) circuit, also known as Sweep Time Control or Anti-Clutter Sea, is a feature found in radar receivers. Its primary function is to automatically reduce the receiver's gain for echoes received from close-range targets and gradually restore full gain for more distant targets. Sea return, or sea clutter, refers to strong, unwanted echoes reflected from the sea surface near the radar antenna. These reflections are typically very strong due to their proximity. By reducing the receiver sensitivity for these close-in echoes, STC effectively "dims" or suppresses the display of sea return on the PPI (Plan Position Indicator) scope, making it easier to detect weaker targets that might otherwise be obscured by the clutter. Therefore, option B is correct because STC specifically *decreases* the appearance of sea return. Option A is incorrect because STC *decreases* sensitivity for close targets, not increases it. Option C is incorrect; bearing resolution is determined by antenna beamwidth, not by STC. Option D is incorrect as STC's purpose is to *reduce* sea return, not increase it.