Final answer:
The blank in the sentence should be filled with the word 'onslaught', indicating a powerful attack that caused the enemy's lines to crumple.
Step-by-step explanation:
The correct word to fill in the blank in the sentence "The enemy's le a harvester." is onslaught, which means a fierce or destructive attack. A retreat is a withdrawal of troops, a fortification is a defensive military construction, and a ceasefire is a temporary suspension of fighting, so these do not fit the context of the sentence which describes an aggressive action.ines crumpled before the mighty onslaught of our attack like so much wheat befor