When a shift occurs from one vowel sound to another, it is:AMonophthongsBDiphthongsCCardinal vowelDPure vowelAnswer: B. Diphthongs Read Explanation: A diphthong is a vowel sound in which the tongue (and often the lips) move from one vowel position toward another within the same syllable.It involves a glide from one vowel sound to another.Examples in English:/aɪ/ as in my, time/ɔɪ/ as in boy/aʊ/ as in nowa) Monophthongs → These are pure vowels where there is no glide or movement; the vowel quality stays the same throughout the sound.c) Cardinal vowel → A reference point vowel in Daniel Jones's system, not about gliding between vowels.d) Pure vowel → Same as monophthong; no shift from one vowel to another. Read more in App