The Himalayan Mountains border India to the north and slightly to the west. The Hindu Kush Mountains border India to the northwest but only account for a very small portion of the Indian border and are largely in Pakistan and Afghanistan. For this question I would say the best answer is the Himalaya Mountains.
The Hindu Kush Mountains border India to the northwest, particularly along its frontier with Pakistan and Afghanistan. Although the Himalayas are often noted, they define northern boundaries, while the Hindu Kush contributes a significant geographical feature to the northwest. Therefore, the correct answer is D. The Hindu Kush Mountains.
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