Answer:
Sonnet 18 is an example of a metaphor.
Step-by-step explanation:
William Shakespeare in his Sonnet 18 has compared the beauty of a young man with summer. In the first line of the sonnet, the young man has been compared with a day in the summer. Both possess the qualities of being 'lovely' and 'temperate'. This is an example of a metaphor in the sonnet. The comparison of the young man and the day of the summer has been prevalent in the sonnet.