In World War I, trenches were dug so that the soldiers could avoid the near constant_____________ from the other side of the line of battle, but not even a trench could protect a battalion from grenades or aerial bombardment.

Considering the above highlighted clues we can reuse the word aerial bombardment/ grenades for the blank.

□ volleys- a number of bullets, arrows, or other projectiles discharged at one time
□ provocations- action or speech that makes someone angry, especially deliberately.
□ fervency- warmth or intensity of feeling
□ imprecations- a spoken curse.
□ goadings- to urge on
□ salvos- a simultaneous discharge of artillery or other guns in a battle

Only A & F fits the bill

IMO A & F

Hope this helps!