Final answer:
The correct answer is C. Premixing.
Step-by-step explanation:
The Venturi Principle is a concept in fluid dynamics that describes how the speed of a fluid increases when it passes through a constricted segment of a pipe or tube.
In the context of foam proportioning, premixing is the method that depends on the Venturi Principle. In this method, foam concentrate is drawn from a container and mixed with water as it passes through a hose connected to the container. The constricted Venturi segment in the hose creates a low-pressure region that draws in the foam concentrate.