Answer: A. Metaphor.
Step-by-step explanation: a metaphor is a figure of speech that consists in a direct comparison between elements that aren't obviously related, often with the function of creating an image in the reader's mind. In the given sentence, we can see an example of a metaphor, specifically in the phrase "the enemy must realize he has awoken a sleeping giant" comparing the consequences of the threat of the enemy with the awakening of a sleeping giant