I think it is b because since it refers to climate vegetation it could be b mostly other answers dont make sense
i hope this helps you
from google:
"The Earth gets hotter as one travels towards the core, known as the geothermal gradient. Geothermal gradient is the amount the Earth's temperature increases with depth, indicating heat flowing from the Earth's warm interior to its surface. On average, the temperature increases by about 25°C for every kilometer of depth"
<span>The answer would be Cultural Change</span>
