Please elaborate more on your question so I can help you
Structural constraint is the answer :)
<span>he theory states that Earth's outermost layer, the lithosphere, is broken into 7 large, rigid pieces called plates: the African, North American, South American, Eurasian, Australian, Antarctic, and Pacific plates. Several minor plates also exist, including the Arabian, Nazca, and Philippines plates. The plates are all moving in different directions and at different speeds</span>
Answer:
light doesn't need a medium through which to travel because the speed of light is experimentally constant
