The appropriate evidence from the text that supports the claim that geostationary satellites must orbit at a specific height above sea level is:
The distance between an orbiting satellite and the object it orbits is related to the satellite's speed.
This statement indicates that for a satellite to maintain a geostationary position—where it orbits the Earth at the same rotational speed as the Earth's rotation (24 hours)—it must be at a specific distance from the Earth. If the height were different, the orbital speed would change, which would no longer allow the satellite to remain above the same point on Earth's surface.