D, T and L can be pronounced independently and correctly, but the words at the beginning of Di Tili are not pronounced correctly. The main problem is that these sounds are emitted from both sides or one side of the tongue base, so there is air leakage or noise. D, T and L all belong to the middle of the tip of the tongue, so they should be pronounced normally on the tip of the tongue. The reason for this problem is that my oral muscles are not tense when I pronounce. For example, when Dida pronounces, the position of the tongue is the same. On the basis of large tongue position, tightening the muscles of mouth and lips can make a normal beep. (oral muscles tighten. Imagine that someone is trying to force you to feed poison, and your lips are tight and you fight back. )