This is a diphthong, a double-vowel sound. The shape the mouth makes changes from the beginning of the word to the end.
这是一个复合元音，双元音。嘴的形状从这个音的开始一直到最后都要变化。
It's pronounced/ɔi/. Did you notice how my mouth changed shape?
它的发音是/ɔi/。你注意到我的嘴型是如何变化的了吗？
Watch. /ɔi/ Now you try. Listen and repeat after me. /ɔi/ /ɔi/
仔细看。/ɔi/现在你来试一下。仔细听然后跟我读。/ɔi/ /ɔi/
Now here are some words which have the/ɔi/sound: choice, noise, boy. Now you try. Listen and repeat: choice, noise, boy.
这里有些含有/ɔi/发音的单词：choice，noise，boy。现在你来试一下。仔细听然后重复：choice，noise，boy。
Good.
很好。