【正确答案】In the production of vowels, there is no obstruction of air as is the case with consonants. Therefore, the description of the vowels cannot be done along the lines of the description of the consonants. To get out of this problem, vowels are normally described with reference to the following criteria:
(1)The part of the tongue that is raised-front, center, or back;
(2)The extent to which the tongue rises in the direction of the palate. Normally, three or four degrees are recognized: high, mid (often divided into mid-high and mid-low) and low;
(3)The kind of opening made at the lips-various degrees of lip rounding or spreading;
(4)The position of the soft palate-raised for oral vowels, and lowered for vowels which have been nasalized;
(5)The opening of the mouth-close, semi-close, semi-open, open;
(6)The length of the sound-long, short.

【答案解析】[解析] 本题考查元音描写的原则。发元音时，没有类似发辅音时产生的气流受阻的现象，因此，通常依据以下几个原则对元音进行描写：舌头抬升的部位、舌头沿上腭抬升的程度、唇的开合度、软腭的位置、嘴的张合度和发音的长度。