While not all land is suitable for agriculture, farmers can use irrigation and fertilizer to make land

Arable lands.

Explanation:

The word arable means to be able to plowed and use for the growth of groping crops. And is a temporal use of the land that can be characterized by the pastures and the meadows and thus is generally under the system of the crop rotation. India has the largest arable land for the farming activities as 1,597 km square, with the U.S and the second and Russia as the third owing to the productivity of the lands. The use of the slash and burn and other cropping techniques makes the lands more arable to the human use and thus can feed the growing population of the country.

I'm pretty sure it's c. extremely gradual but not 100% sure though.

Ithink the best answer is d increased stability of all other biomes