Thoreau included the following sentence in walden: "there is some of the same fitness in a man's building his own house that there is in a bird's building its own nest."

which of the following statements rephrases his literal comparison as a metaphor?
a. a man building his house is like a bird building his nest.
b. a man's house is his nest.
c. every bird is an architect and builder of a nest.
d. between a human house and an avian nest, there is absolutely no difference in architectural skill.