<span>By combining it with its wild respective realtive to avoid acquiring diseases. or It can save a crop plant by altering its structure, so it can repel diseases</span>
I believe the answer to this question is D, I am not sure though.
The gradual movement of the continents across the Earth’s surface throughout geological time.
Plants use carbon to live, just like humans use oxygen. It's a virtuous cycle sine humans breathe oxygen and expel carbon, and plants "breathe" carbon and expel oxygen.
If plants weren't there to "breathe" the carbon, it would just sit in the world, and build up in the atmosphere.
