The situation wherein you would double the final consonant in a base word before adding a suffix is option D. When the base word ends with consonant + vowel + consonant and the suffix begins with a vowel. For example: the word, "FAT" when we add the suffix -er and -est, it becomes "fatter" and "fattest". The letter "T" is doubled, then add the vowel suffix.
D. when the base word ends with consonant + vowel + consonant and the suffix begins with a vowel
Explanation:
If you study English, you have heard of words ending in "consonant + vowel + consonant" (or CVC). These endings have a simple half rule: when the suffix begins with a vowel, the last consonant of the base word must be duplicated. Example: The base word is "stop" and the word "ed", when you add the base word with the suffix, the last letter "p" of the base word must be duplicated, becoming "stopped".
