ANS:B - aqueduct

Aquaduct:-When canal runs above that drainage then it called aqueduct. The only condition for constructing aqueduct is that the HFL of drainage should be below the bottom of the canal.

Syphon Aqueduct: When the distance between the bottom of canal and bed of drainage is less then there is a possibility of drainage water to enter the canal. To avoid this problem, the drainage bottom is artificially lower down below the canal this construction is called Syphon Aqueduct.