A hose appliance that combines two or more hose lines into one is called what?

The correct choice refers to a hose appliance known as a "Wye." A Wye is specifically designed to split a single hose line into two separate lines, allowing for the distribution of water flow to multiple locations simultaneously. This is particularly useful in firefighting scenarios where two lines might be needed to combat a fire more effectively or in different directions.

In the context of firefighting, a Wye fitting allows firefighters to take a single source of water and utilize it in two different operational areas without sacrificing pressure. This is crucial for maintaining adequate water supply and managing flow more efficiently during fire suppression efforts.

The other options listed serve different purposes: a Yoke typically refers to a type of connection or support structure in various contexts, a Siamese fitting combines two hoses into one but does not split a single line into two, and a Coupling is a device used to connect two hoses together. Understanding these distinctions helps clarify the roles of each appliance in firefighting operations, supporting effective technique and safety.