Final answer:
When adding a suffix to a one-syllable word that ends in S, F, or Z, the final consonant is doubled.
Step-by-step explanation:
When adding a suffix to a one-syllable word that ends in S, F, or Z, the final consonant is doubled. For example, when adding the suffix -ed to the word fuss, the final 's' is doubled, resulting in fussed. Similarly, when adding the suffix -ing to the word caress, the final 's' is doubled, resulting in caressing.