求一个很基础的问题:a和an的区别,谢谢

a后接什么
an后接什么
比如说一场事故,用a还是an呢,谢谢!
...
什么叫辅音,什么叫元音啊,比如说谢谢

a D [di:] 一个D (B、C、G、J、K、P、Q、T、U、V、W、Y、Z前也用a)
an F [ef] 一个F（A、E、H、I、L、M、N、O、R、S、X前也用an）

元音：发音响亮，是乐音；口腔中气流不收阻碍；是构成音节的主要音。英语中有20元音。

辅音：发音不响亮，是噪音；口腔中气流受到阻碍；不是构成音节的主要音。英语中有28辅音。

元音：(注意：下面空方括号是电脑无法输入的音标)

1) [i:] sea, he, see, piece, ceiling

2) [i] sit, build, miss, myth

3) [e] bed, desk, head,

4) [ ] bad, land, bank, stamp

5) [a:] car, fast, class, plant, calm, aunt

6) [ ] hot, want

7) [ ] door, more, sport, ball, warm, author, court, bought, caught

8) [u:] good, who, blue, soup,

9) [u] look, put, women, could

10) [ ] cup, come, blood, rough

11) [ ] girl, work, serve, nurse

12) [ ] cadre, ago, forget, polite, dollar, doctor, famous, Saturday

13) [ei] cake, they, play, eight, great,

14) [ai] bike, die, neither, light, try, find, height, eye

15) [ ] phone, cold, boat, soul, grow

16) [au] house, town