The correct answer is: a) Alluvial soils.
Alluvial soils are the most common type of soil in the coastal plains of Andhra Pradesh. They are formed by the deposition of sediments from rivers and streams. Alluvial soils are typically fertile and well-drained, making them ideal for agriculture.
Black soils are another type of soil that is found in the coastal plains of Andhra Pradesh. They are formed by the weathering of volcanic rocks. Black soils are rich in iron and magnesium, and they are well-suited for growing crops such as rice and cotton.
Red soils are also found in the coastal plains of Andhra Pradesh. They are formed by the weathering of granite rocks. Red soils are poor in nutrients, but they are well-drained and suitable for growing crops such as millet and sorghum.
Laterite soils are found in the drier parts of the coastal plains of Andhra Pradesh. They are formed by the weathering of limestone rocks. Laterite soils are poor in nutrients and are not well-suited for agriculture.
In conclusion, the coastal plains of Andhra Pradesh are predominantly composed of alluvial soils. These soils are fertile and well-drained, making them ideal for agriculture.