The correct option is C Communication trenches were dug perpendicular to the trenches.
In trench warfare, armies on both sides dug pits to defend themselves and attack the enemies. Each trench was dug in a zigzag manner, preventing the enemies standing at one end from firing more than a few yards down its length. The trenches were connected to each other and to the rear by a series of communications trenches dug perpendicular to them. The rains made the trenches muddy, which further made the lives of soldiers difficult.