Vowel sounds are differentiated by a number of factors,which is

Vowel sounds are differentiated by a number of factors,which is not belong to these factors?
A、the position of the sound in the mouth
B、the openness of the mouth
C、the shape of the lips
D、the length of the vowels
【正确答案】：A
【题目解析】：Vowel sounds are differentiated by a number of factors：the position of the tongue in the mouth, the openness of the mouth, the shape of the lips, and the length of the vowels.