Which of the following best describes monophthongs?

Monophthongs are defined as single vowel sounds that maintain a single, stable sound quality throughout their production. This means that they do not involve a change in vocal tract configuration or tongue position as they are articulated. The term "monophthong" itself comprises the prefix "mono-" meaning single, and "phthong," related to sound or voice. When producing a monophthong, the tongue remains in a fixed position, creating a pure vowel sound, such as the vowel sounds in "cat" or "bed."

Understanding this definition helps clarify why this choice accurately describes monophthongs. The other options revolve around characteristics that do not align with the static nature of monophthongs. For example, the concept of vowels gliding between two positions relates specifically to diphthongs, which involve movement and a change in vowel quality. Similarly, vowels produced with restriction of airflow pertain more to consonants or certain types of phonetic sounds, and consonant-like vowel sounds would refer to vowel qualities that imply a blend with consonant features rather than the pure, distinct qualities of monophthongs.