The change of a simple vowel to a diphthong,often caused by the influence of neighboring consonants. 元音，割裂一个单元音向一个双元音的转变，常由临近辅音影响所致。
One day in the class I could not pronounce a diphthong - not opening my mouth wide enough - since I was from the Northeast, no matter how many times Teacher Zhang corrected me. 有一次，张老师纠正我的发音，说我这个东北人，双元音口形总是张不开，一再娇正也发不好。
