The correct answer is A) Coastal plains.
The coastal plains of Karnataka are the most fertile region in the state. They are located in the southern part of the state and are bounded by the Arabian Sea to the west and the Western Ghats to the east. The coastal plains are a major rice-producing region and are also home to a number of other crops, including sugarcane, coconut, and mango.
The Malnad region is located in the northern part of Karnataka and is characterized by its high hills and dense forests. The Malnad region is not a major rice-producing region, but it is home to a number of other crops, including coffee, tea, and cardamom.
The Deccan Plateau is located in the central part of Karnataka and is a plateau region with a relatively dry climate. The Deccan Plateau is not a major rice-producing region, but it is home to a number of other crops, including cotton, sorghum, and millet.
The Northern plains are located in the northern part of India and are a major rice-producing region. However, the Northern plains are not located in Karnataka.