Answer:
D. The fact that his foe has apparently been killed in the end.
Step-by-step explanation:
William Blake's "A Poison Tree" is a short four-lined poem of four stanzas that talks about the evils of hatred. The poem presents two cases of hatred- one against a good friend and another against a foe.
The speaker reveals that the hatred that he had against his friend was resolved when he told that friend about it. On the other hand, the "wrath" that he had against his foe went unresolved when he did not tell him about it. And the consequence of this wrath was 'fruitful' for the speaker when the speaker revealed that his foe lay "outstretched beneath the tree", suggestive of that person's death.
Thus, the correct answer is option D.