关于 剑桥字典中有 [I],[ i ] 和[i:]
请参考
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WEAK VOWEL
WEAK VOWEL. In phonetics, a VOWEL that normally occurs only in unstressed syllables. There are two weak vowels in English SCHWA /ə/, as in the unstressed syllables of above and sofa, and short i /ɪ/, as in the unstressed syllables in RP example and Sophie.
---------摘自 http://www.encyclopedia.com/doc/1O29-WEAKVOWEL.html
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好像只有英音有这种现象,( 美音没有分这么细, 一律读长元音):
[I] 短元音
[ i ] 弱元音 The weak vowels are confined to weak, unstressed, syllables. 是指在非重读音节中的读音
[i:]长元音