A parabolic antenna is very efficient because:

The high efficiency and massive gain of a parabolic antenna come directly from its geometric shape. A parabola has the unique mathematical property of reflecting all incoming parallel waves to a single converging spot, known as the focal point. By placing the feed element—often a horn or a small dipole—exactly at this focal point, the antenna captures nearly all the intercepted RF energy. The reflector acts like a massive funnel for radio waves. The other options are incorrect because while horns and dipoles can be used as the actual feed, they are not the reason the parabolic shape itself is efficient. Furthermore, impedance matching is always required regardless of the antenna type.