The correct answer is: Zanskar.
Zanskar is a valley in the Indian state of Jammu and Kashmir. It is located in the Ladakh region, and is one of the most remote and sparsely populated areas in India. The Zanskar River flows through the valley, and in winter, the river freezes over, creating a natural ice bridge that trekkers can use to cross the valley.
The Zanskar Valley is a popular destination for trekking, and is known for its stunning scenery and challenging terrain. The valley is also home to a number of Buddhist monasteries, which are a popular tourist attraction.
The other options are incorrect because they are not valleys in the Zanskar region. Option A, Aru, is a valley in the Lahaul and Spiti district of Himachal Pradesh. Option B, Nubra, is a valley in the Ladakh region of Jammu and Kashmir. Option C, None of these, is incorrect because it is not a valley in the Zanskar region.