【正确答案】正确答案：As in the production of vowels, the air stream meets with no obstruction, they cannot be classified in terms of manner of articulation or place of articulation as consonants. Vowels can be classified by the following factors;(2 points) (1)the position of the tongue in the mouth—front, central, back;(2 points) (2)the openness of the mouth—close, semi-close, semi-open, open;(2 points) (3)the shape of the lips—rounded, unrounded;(2 points) (4)the length of the vowels—long, short.(2 points)

【答案解析】解析：考查元音分类的标准。元音常根据舌位的高低、口型的大小、唇形、元音的长度等来分类。根据舌位的高低，元音可分为前元音，中元音和后元音；根据口型的大小可分为闭元音，半闭元音，半开元音和开元音；根据唇形可分为圆唇音和展唇音；根据元音的长度可分为长元音和短元音。