Which of the following is not listed as a vowel sound in the example set provided?

• A. /u/
• B. /a/
• C. /o/
• D. /p/

Answer: (D)

Vowel sounds are produced with an open vocal tract and relatively little constriction, allowing the voice to resonate and often forming the nucleus of a syllable. In the example set, the sounds /u/, /a/, and /o/ fit this pattern because they can function as vowel sounds and are produced with an open mouth position that supports sustained voicing. The sound /p/ is different: it is a consonant, specifically a voiceless bilabial stop, made by briefly closing the lips to stop the airflow and then releasing it. That brief burst of air and the constricted articulate point do not create a sustained, resonant vowel sound, so it is not listed as a vowel in the example set.