Final answer:
The correct option is: B) Speed of Light. Earth-based observers measure the speed of the approaching landing craft as the speed of light. This means that light travels at a constant speed throughout the universe, and it is the same for all observers, regardless of their motion or reference frame.
Step-by-step explanation:
The speed that Earth-based observers measure for the approaching landing craft is the Speed of Light. The speed of light is a fundamental constant in physics, denoted by the symbol 'c'. It is approximately equal to 299,792,458 meters per second in a vacuum. This means that light travels at a constant speed throughout the universe, and it is the same for all observers, regardless of their motion or reference frame.
The correct option is: B) Speed of Light. Earth-based observers measure the speed of the approaching landing craft as the speed of light. This means that light travels at a constant speed throughout the universe, and it is the same for all observers, regardless of their motion or reference frame.