What type of system predominantly utilizes static air for functioning?

The static port is the correct answer, as it is specifically designed to measure the ambient atmospheric pressure around the aircraft. This is crucial for determining altitude and vertical speed, enabling the aircraft's altimeter and other flight instruments to function accurately. The static port allows atmospheric pressure to be captured while preventing airflow from directly affecting its readings, which is essential for maintaining precise instrument performance.

In contrast, while the pitot tube also plays a vital role in aviation by measuring dynamic pressure to calculate airspeed, it primarily relies on the movement of air, not just static air. The angle of attack sensor is designed to detect the angle between the oncoming air and the aircraft's wing, focusing more on dynamic conditions rather than static pressure alone. The rate-of-climb indicator assesses the vertical speed of the aircraft by utilizing both static and dynamic pressures, but it does not predominantly use static air. Thus, the static port stands out as the system that predominantly utilizes static air for its operation.