While the Trench Warfare of World War I Was a Bloody

While the trench warfare of World War I was a bloody ordeal,overall mortality rates were not as high as they might have been because

A) officers arranged for men under their command to retreat if battles became excessive.
B) soldiers from both sides tended to avoid shooting at one another if possible.
C) the trenches provided good shelter both from enemy fire and the elements.
D) disease was kept to a minimum through modern medical advances.