Which of the following is true?

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

Which of the following is incorrect?

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

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.

... 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.