How did the new weapons of war influence the way soldiers fought in battle? In other words, why was trench warfare the only possible way to fight?

Trench warfare is a type of land warfare using occupied fighting lines largely comprising military trenches, in which troops are well-protected from the enemy's small arms fire and are substantially sheltered from artillery. Trench warfare became archetypically associated with World War I (1914–1918), when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914.[1]

d is definitely the answer