during world war i, the second phase in battles that crossed enemy lines and approached trenches was heavy…

Brief Explanations:

In World - War I trench warfare, after initial heavy bombardment to weaken enemy defenses, the second phase when crossing enemy lines and approaching trenches was an infantry attack. Sniper fire was more of a harassing or precision - targeting tactic throughout the battle, and aerial bombing was not the typical second - phase action in this context.

Answer:

D. infantry attack