The retina; I may be wrong.
The answer would be : <span>It is a well supported explanation which cannot become a law.
A law and a theory are different you know. In fact, the law is universel. This applies for everything unlike a theory which explains in particular why something is happening.
Any doubts ?
Hope this helps !
Photon</span>
The correct answer is the tundra.
I would say d, they can’t move and they are remains from the past