Final answer:
The sentence 'He is as fast as a horse' is a simile, as it compares the speed of someone to that of a horse.
Step-by-step explanation:
The sentence, 'He is as fast as a horse,' is an example of a simile. A simile is a figure of speech that compares two unlike things using the words 'as' or 'like'.
In this case, the student is comparing the speed of someone to that of a horse. The use of 'as' signifies the comparison.
Learn more about simile