名词前的a,an到底怎么分?知道是元音字母aeiou,可音标里哪些算啊.初三党←_←

单元音：
[e] yes yellow bed
[ae] cat bad dad
[a:] are car far
[כ] pot got dog
[כ:] call tall or
[۸] cut nut but
[3:]curtain further fur
[ə]mother color cooler
[i] ink big pig
[i:] jeep tea eat
[u] good book look
[u:] cool zoo tool
双元音：
[ei] age eight make
[ai] ice bike nice
[כi]toy oil boy
[əu] old joke gold
[au] cloud mouth cow
[εə] air fair chair
[iə] ear near year
[uə] cure dure pure

这个不是初三的问题。。。我初一就学了！不，应该是小学了！

看音标最前面的一个字母啊