The plains of India are a significant geographical feature of the country. They cover a vast area and are divided into two major sections - the Northern Plains and the Coastal Plains. Therefore, the correct answer to this question is option 'C' - Both.

Northern Plains:
The Northern Plains of India are located in the northern part of the country and are one of the most fertile regions. They are formed by the alluvial deposits brought by the rivers originating from the Himalayas. The major rivers that traverse through this region are the Ganges, Yamuna, Brahmaputra, and their tributaries. These rivers, along with the fertile soil, make the Northern Plains suitable for agriculture. The region is known for its extensive cultivation of crops such as wheat, rice, sugarcane, and tobacco. The cities of Delhi, Lucknow, Kanpur, and Patna are situated in the Northern Plains.

Coastal Plains:
On the other hand, the Coastal Plains of India are located along the eastern and western coasts of the country. The Eastern Coastal Plains are formed by the alluvial deposits of the rivers like the Mahanadi, Godavari, Krishna, and Kaveri. These plains are known for their fertile soil and are suitable for agriculture. The major cities on the Eastern Coastal Plains include Chennai, Visakhapatnam, and Puri. The Western Coastal Plains are narrower compared to the Eastern Coastal Plains and are formed by the deposition of sediments brought by the rivers like the Narmada, Tapi, and Periyar. These plains are characterized by the presence of lagoons, backwaters, and estuaries. The major cities on the Western Coastal Plains include Mumbai, Mangalore, and Kochi.

Conclusion:
In conclusion, the plains of India can be categorized into two major sections - the Northern Plains and the Coastal Plains. The Northern Plains are formed by the alluvial deposits of rivers like the Ganges and Yamuna, while the Coastal Plains are formed by the alluvial deposits of rivers like the Mahanadi and Narmada. Both these regions have fertile soil and are suitable for agriculture.