The correct answer is: A. Syphon
A syphon is a pipe that carries water under pressure, and it is designed so that its F.S.L. does not touch the underside of the supporting structure. This means that the water in the syphon is always above the level of the ground, and it is this pressure that keeps the water flowing.
Aqueducts are structures that carry water over a long distance, and they are typically built on arches or piers. Super passages are structures that carry water over a short distance, and they are typically built on embankments or bridges. Syphon-aqueducts are a combination of a syphon and an aqueduct, and they are used to carry water over long distances when there is a natural drainage in the way.
In this case, the canal is flowing under pressure, and it is carried below a natural drainage such that its F.S.L. does not touch the underside of the supporting structure. This means that the structure so provided is a syphon.