1, [I:] is a long sound, which is emitted by the mouth with a sharp front, and the mouth is very flat, and the lips smile at both sides of Zhang Kaicheng.
[I] is a short sound, which comes from the throat and has a slightly narrow mouth. When you make this sound, it should be short and powerful.
3. [E], the tip of the tongue touches the lower teeth, and the front of the tip of the tongue is slightly raised. Don't open your mouth too wide, and the distance between your upper and lower teeth would rather be smaller.
4、[? ], open your mouth, open it wide and try to relax. You can exaggerate a little when you start practicing.
5.[ei], the mouth shape slides from [e] to [i]. In the process of pronunciation, the jaw closes upwards and the tongue position rises slightly.