Final answer:
The sentence, 'He was as tough as nails,' is an example of a simile.
Step-by-step explanation:
The sentence, "He was as tough as nails," is an example of a simile. A simile is a figure of speech that directly compares two unlike things using the words 'like' or 'as'. In this sentence, the toughness of the person is being compared to the toughness of nails using the word 'as'.
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