In texts or speech, it is common to use objects, animals, ideas, etc. to describe a different element, this occurs through the use of simile or metaphor that are two rhetorical figures that use comparison to describe a subject.
In the case of comparing a person as a weasel, the purpose of the author is not to state the person is a small mammal but to show the person has some feature weasels also do. According to this, it is likely the writer means "The person is sneaky" because weasels move sneakily and seem to be very furtive or sneaky and this is a feature people can also show.
Your answer is NOT (A) becuase weasel doesnt mean elegant. (B) would be the correct one. (C) They could have used a better word instead of sneaky. And finally (D) the person is not a small mammal. i mean possibly but there is no context.
