Answer: The construction of trenches made it hard for either side to advance.
Step-by-step explanation:
The statement that explains the reason why the western front turned into a stalemate during World War I is that the construction of trenches made it hard for either side to advance.
During World War 1, trench warfare was vastly used as it gives the soldiers protection from enemies. Soldiers were unable to cross the area that was between the trenches as the land was mined territory and also they were was subjected to gunfire, and artillery.