Final answer:
Trenches in World War 1 were built with the intent to provide protection, create a defensive line, and establish communication and supply systems.
Step-by-step explanation:
The intent of building trenches in WW1 was all of the above. Trenches were constructed to provide protection for soldiers from enemy fire, create a defensive line to prevent enemy advancement, and establish a system of communication and supply. The new technologies of war, such as trenches, machine guns, mines, and modern rifles, made it more effective to entrench oneself and defend a position rather than charge and try to take the enemy's position.