试题题干
Fill in each of the following blanks with a word or an expression.
In terms of lip rounding ,vowels are classified into rounded vowels and 
vowels .
参考答案
试题解析
In terms of lip rounding ,vowels are classified into rounded vowels and unrounded vowels . 根据口形，元音被分成圆唇元音和非圆唇元音。