The correct answer is - b. less arable land.
The cleaning of the land by its natural cover, be it forests or grasslands, has very negative effect on the environment. The soil loses its natural protection so it can erode easily, the biodiversity in both the flora and fauna will be decimated, and there will be bigger CO2 emission into the atmosphere as there will be no plants to consume it for the process of photosynthesis.
The purpose of the clearing of the land is usually two things, building or increasing the area of arable land for the agriculture. So the clearing of the land doesn't mean less arable land, but the opposite, more arable land.