unit 6 english vowels: back vowels / :/ / 05 / /u:/ /u/ / 00
3.back vowelsppt
purevowels frontvowels前元音centralvowels中元音backvowels后元音
unit 6 english vowels: back vowels / :/ / 05 / /u:/ /u/ / 00
unit 6 english vowels: back vowels / :/ / 05 / /u:/ /u/ / 00