I already answered the question but here it is again:
The correct answer is B. to keep readers from realizing at the start that no humans are present.
Indeed, Bradbury’s story is intended to warn readers that the inevitable consequence of an all-out nuclear war is the extinction of the human race. His story is inspired by the much earlier poem from American poetess Sarah Teasdale, who wrote the poem of the same title in the aftermath of World War I, which until then had been the most devastating conflict in the history of the world at that time. Since the house is a mechanical entity; it stresses the fact that it was built by humans but since no humans are present anymore, their absence is all the more noticed and the, dramatic impact for readers is stronger and everlasting.
