Answer: A) Metaphor.
Explanation: a metaphor is a figure of speech that consists in making a direct comparison between elements that aren't obviously related, in order to create an image in the reader's mind. In the given sentence, we can see a clear example of a metaphor that compares Janet's eyes to two bright emeralds (without using the words "like" or "as" to make the comparison), so the correct answer is option A.