The major consideration in distinguishing the major regional dialects is

1) vocabulary
2) the pronunciation of consonant sounds
3) the pronunciation of vowel sounds
4) the frequency which terms like "ya'll" are used

The major consideration in distinguishing the major regional dialects is the pronunciation of vowel sounds. Dialects are usually divided by pronunciation and you can identify person by that feature. 

The best answer to the incomplete sentence above would be the third statement. The major consideration in distinguishing the major regional dialects is the pronunciation of vowel sounds. Some dialects have melodic differences compared to pronouncing words.