English: How to Pronounce UH as in BUTTER [/ ] vowel
https://www.youtube.com/watch?v=sJupiMmsbx0
American Accent 60 Words with "uh" [/ ] Vowel Sound - American English Pronunciation Lesson
https://www.youtube.com/watch?v=ausxODBl6m0
2. ago, sofa
English: How to Pronounce the Schwa(英語中非重讀音節的元音) [?] -- American Accent https://www.youtube.com/watch?v=rM9NxK74JSE