The first sound: uh as in pull is how it is written. However in practice, I find it to have some of the oo as in boo mixed in. luh-uh-uh-uh as in lure. In slow motion: ooooo uuuuuuuhhhh rrrr. So the sound goes from the uh or oo sound, where the lips are more rounded, to the schwa, where the mouth is very relaxed and the tongue is very relaxed, to the rr, rr, where the lips come in a little bit, the then push out a little bit, and the throat closes a tiny bit here to make the sound come from uhh.
第一个音，虽然写做[u]（pull一词中的[u]音），但是念的时候却混合了一些[ɔ]的成分（boo一词中的[ɔ]音）。我们来试着念一下lure一词中的[uə]音，用慢动作来念就是：ooooo uuuuuuuhhhh rrrr。也就是说，[uə]这个音是从唇形较圆[u]或者说[ɔ]音，到嘴型和舌头都十分放松的[ə]音，再到嘴唇略微向中间聚拢并向前突出，而喉咙处略微缩紧的R音。