An inverted siphon is a type of pipe that is used to carry water over an obstacle. It is designed generally for one pipe. The pipe is laid in a U-shape, with the bottom of the U being below the obstacle. The water flows through the pipe and out the top of the U.
The inverted siphon is a very efficient way to carry water over an obstacle. It is also very versatile, and can be used in a variety of applications.
The other options are incorrect because they do not represent the number of pipes that are typically used in an inverted siphon.