元音

我在作a/an的改错时老是错，不知道元音到底有哪些，还有这个区别：

an unusual      a unique

自己很困惑，上网查了下也没找到什么权威的东东，请哪位大侠出来帮我总结下，感激不尽！

Phonological elements are instored in the mental lexicon. You have to determine how to pronounce the prefix / u- / as in 'university' or 'unique', then, decide to link which article to it.

If the sound comes out like /ju/, link 'a-' to it; if the sound comes out like /a/, link 'an-' to it.

some examples:

a university / a unique / a united

an under-water apparatus / an underlying method

An MBA program (the first sound that comes out like /ai/)

An NP (the first sound that comes out like /ai/)