... vowels are the ones in the production of which the lips may be spread out so as to leave a long narrow opening between them.

According to the..., vowels can be rounded, neutral, or unrounded.

In the articulation of the... sound, the central part of the tongue is raised toward the palate.

Which of the following is incorrect?

A/an... vowel is the one in the production of which one part of the tongue comes close to the palate without touching it and the air passage is narrow, but not so much as to form a consonant.

Which of the following is true?

... are sounds articulated by the lower lip against the upper teeth.

may be defined as one or more speech sounds forming a word or part of a word, containing one vowel sound, with or without a consonant or consonants, and uttered at a single effort.