The correct answer is A: Cardioid. A single-turn, terminated loop such as a pennant antenna creates a cardioid (heart-shaped) radiation pattern. The termination makes the loop unidirectional with a single null. A terminated loop (like a pennant antenna) is a loop antenna with a termination resistor. The termination absorbs the wave traveling in one direction, making the antenna unidirectional. This creates a cardioid pattern - strong in one direction with a null in the opposite direction. The cardioid pattern is ideal for direction-finding because it has a single, well-defined null that clearly indicates direction. This is different from an unterminated loop, which would have a bidirectional figure-eight pattern. The termination is what creates the cardioid pattern.