The correct answer is: A. Martand Canal
The Martand Canal is the oldest canal in the Kashmir valley used for irrigation. It was built by the ancient king Lalitaditya Muktapida in the 8th century AD. The canal is about 100 kilometers long and irrigates a large area of land in the Kashmir valley.
The Shakul Canal is a canal in the Kashmir valley that was built in the 16th century AD. It is about 50 kilometers long and irrigates a large area of land in the Kashmir valley.
The Zainagir Canal is a canal in the Kashmir valley that was built in the 17th century AD. It is about 30 kilometers long and irrigates a large area of land in the Kashmir valley.
The Lalkul Canal is a canal in the Kashmir valley that was built in the 18th century AD. It is about 20 kilometers long and irrigates a large area of land in the Kashmir valley.
The Martand Canal is the oldest canal in the Kashmir valley because it was built in the 8th century AD. The Shakul Canal, the Zainagir Canal, and the Lalkul Canal were all built later, in the 16th, 17th, and 18th centuries AD, respectively.