The correct answer is: C. Light to dark brown
The color of soil in the low hill soil zone is light to dark brown. This is because the soil in this zone is rich in organic matter, which gives it a brown color. The organic matter in the soil comes from the decomposition of plants and animals. The more organic matter in the soil, the darker the color of the soil.
The other options are incorrect because they do not accurately describe the color of soil in the low hill soil zone. Option A, light grey to brown, is too light in color. Option B, red to brown, is too dark in color. Option D, dark brown, is too specific and does not accurately describe the range of colors that can be found in soil in the low hill soil zone.
In conclusion, the color of soil in the low hill soil zone is light to dark brown. This is because the soil in this zone is rich in organic matter, which gives it a brown color. The organic matter in the soil comes from the decomposition of plants and animals. The more organic matter in the soil, the darker the color of the soil.