The double consonant rule applies when you add ((a)) a suffix beginning with a vowel to a base word ending with two vowels and a consonant. ((b)) a suffix beginning with a vowel to a base word ending with consonant + vowel + consonant. ((c)) a suffix beginning with a vowel to a base word ending with a consonants + a vowel. ((d)) a suffix beginning with a consonant to a base word ending with two consonants.