Cattle contribute directly to topsoil loss by trampling the ground over and over again. The soil they tramp down becomes compacted and hard, especially if there is clay in it. Then, when it rains, this compacted soil is less able to absorb water, so the water simply runs off the land, taking the top layer of soil with it. Cattle also eat all the perennial grasses (grasses that normally come back year after year), and this allows weeds and tougher shrubs to spread. The new weeds do not anchor the topsoil as well as the grasses, so wind and rain can take it away more easily. Cattle create topsoil _.
A. abundance
B. instability
C. perfection
D. pollution
