The correct answer is: A. Doon valley.
A tectonic valley is a valley formed by the movement of tectonic plates. The Doon valley is a tectonic valley located in the Indian state of Uttarakhand. It is a long, narrow valley that is surrounded by mountains. The valley is home to the city of Dehradun, which is the capital of Uttarakhand.
The Kashmir valley is a valley located in the Indian state of Jammu and Kashmir. It is a large, fertile valley that is surrounded by mountains. The valley is home to the city of Srinagar, which is the summer capital of Jammu and Kashmir.
The plains of Aksai Chin are a high-altitude plateau located in the eastern Ladakh region of India. The plateau is a part of the Tibetan Plateau and is located between the Karakoram Range and the Kunlun Mountains. The plateau is sparsely populated and is home to a number of nomadic tribes.
None of the above options are tectonic valleys.