1000-hours/sounds-of-american-english/3.1.4-u.md
<span class="pho">u</span> 这个元音，也被称为 “圆元音”（round vowel），是因为说它的时候，嘴唇要略微缩成一个圆形，且嘴唇还要略微凸出。不过，由于这个元音在地球上的任何语言都存在，并且还几乎是一模一样地用，所以，大家说起来都不费劲。
有一个很小的细节值得注意，短元音 <span class="pho">ʊ</span> 其实就算不把嘴唇弄圆也可以发出，但长元音 <span class="pho">uː</span> 就不行。所以，<span class="pho">uː</span> 发声相对于短元音 <span class="pho">ʊ</span> 嘴唇总是相对更圆更凸出一点点。
请试着比较一下以下词对：
- book <span class="pho alt">bʊk</span><span class="speak-word-inline" data-audio-us-male="/audios/book-us-male.mp3" data-audio-us-female="/audios/book-us-female.mp3"></span> ⭤ boot <span class="pho alt">buːt</span><span class="speak-word-inline" data-audio-us-male="/audios/boot-us-male.mp3" data-audio-us-female="/audios/boot-us-female.mp3"></span>
- cook <span class="pho alt">kʊk</span><span class="speak-word-inline" data-audio-us-male="/audios/cook-us-male.mp3" data-audio-us-female="/audios/cook-us-female.mp3"></span> ⭤ cool <span class="pho alt">kuːl</span><span class="speak-word-inline" data-audio-us-male="/audios/cool-us-male.mp3" data-audio-us-female="/audios/cool-us-female.mp3"></span>
- food <span class="pho alt">fʊd</span><span class="speak-word-inline" data-audio-us-male="/audios/food-us-male.mp3" data-audio-us-female="/audios/food-us-female.mp3"></span> ⭤ foot <span class="pho alt">fuːt</span><span class="speak-word-inline" data-audio-us-male="/audios/foot-us-male.mp3" data-audio-us-female="/audios/foot-us-female.mp3"></span>
- good <span class="pho alt">gʊd</span><span class="speak-word-inline" data-audio-us-male="/audios/good-us-male.mp3" data-audio-us-female="/audios/good-us-female.mp3"></span> ⭤ goose <span class="pho alt">guːs</span><span class="speak-word-inline" data-audio-us-male="/audios/goose-us-male.mp3" data-audio-us-female="/audios/goose-us-female.mp3"></span>
- look <span class="pho alt">lʊk</span><span class="speak-word-inline" data-audio-us-male="/audios/look-us-male.mp3" data-audio-us-female="/audios/look-us-female.mp3"></span> ⭤ loop <span class="pho alt">luːp</span><span class="speak-word-inline" data-audio-us-male="/audios/loop-us-male.mp3" data-audio-us-female="/audios/loop-us-female.mp3"></span>
另外，在《剑桥英语发声词典》中，这个音在非重音音节时被标注为 <span class="pho">u</span>，是个轻元音，和 <span class="pho">i</span> 一样，只出现在非重音音节之中。之前见到过的例子是 situation <span class="pho alt">ˌsɪtʃ·uˈeɪ·ʃən</span><span class="speak-word-inline" data-audio-us-male="/audios/situation-us-male.mp3" data-audio-us-female="/audios/situation-us-female.mp3"></span>。
美音的儿化音 <span class="pho">ʊr</span> 对应着英音的 <span class="pho">ʊə</span>，比如 poor <span class="pho alt">pʊr</span> <span class="speak-word-inline" data-audio-us-male="/audios/poor-us-male.mp3" data-audio-us-female="/audios/poor-us-female.mp3"></span> —— 不过请注意，这个词的英音可不是 <span class="pho alt">pʊə</span>，而是 <span class="pho alt">pɔː(r)</span><span class="speak-word-inline" data-audio-uk-male="/audios/poor-uk-male.mp3" data-audio-uk-female="/audios/poor-uk-female.mp3"></span>。
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