Based on this excerpt, from the poem "Mending Wall", by Robert Frost, the option that best describes the effect of the metaphor on the overall meaning in this excerpt is B. It gives apple trees the qualities of grazing animals to emphasize that the wall is unnecessary.
The narrator's neighbor repeats his father's words and traditions 'Good fences make good neighbors'. He thinks that mending the wall is being practical and doesn't want to hear the narrator's opinion against its utility. The narrator uses metaphors to describe his apple trees as grazing animals, which they are not.