pull: /pul/ (UK), /pʊl/ (US)
Hence, there are three vowels which I consider the same. (I consider these three vowels all to be /u/ (UK) as in 'pull'. I have watched the videos teaching pronunciation on YouTube. But I can't distinguish these three vowels.
更新1:
And does /ʊ/ sound like /ə/ or /u/? I think it looks like /u/ so it would sound like /u/ rather than /ə/. But I heard the video pronounce it like /ə/ rather than /u/ and the video didn't say what it sounds like.