英语音标[3:]与[e]发音有什么区别?

[e][ə][3:]这三个音发音时的舌头部位有点区别:\x0d1.[e]前元音中的舌尖音,舌尖抵下齿,舌前部向硬腭抬起成拱形,但不接触硬腭.双唇向两边咧开,口形扁平似微笑；发音时没有摩擦.上、下齿之间的距离约能容纳一根牙签,发音时舌尖部位最高.如单词:bet set get let debt met pet wet yes yet member yesterday leg egg bed desk pen elephant seven eleven\x0d2.[ə]中元音,口形与唇成自然状,肌肉放松,口腔半开,发音时舌头中部最高,短元音.如单词:ago about asleep above again among mother brother doctor teacher never danger sugar order butter picture\x0d3.[3:]平舌音,是由旧国际音标中的[ə:]改过来的,发音规则:口腔在半开状态,唇向两边咧开,舌头平放,长元音.如单词:girl shirt hurt burn bird nurse work worm curse world dirty skirt thirsty worst person curtin serve early