(C) Bhopal Lake
Bhopal Lake, one of the largest artificial lakes of its time, was built in the 11th century for water conservation.
The source passage (Hydraulic Structures in Ancient India box) directly states: "In the 11th Century, Bhopal Lake, one of the largest artificial lakes of its time was built." Sambhar and Chilka are natural lakes; Wular is also a natural lake. Bhopal Lake is the only artificial one mentioned, built in the 11th century.