How to pronounce [d]:
Make an obstacle by keeping your tip of tongue touch the upper alveolar ridge, compress air in your mouth and then release the airflow by quickly break through the obstacle without vibration of the cord. The sound of [d] is similar to the “d” in the English word “down”.
How to pronounce [t]:
The position of articulation is the same as that of [d] but airflow is pushed out forcibly from mouth without vibration of the cord. The sound of [t] is similar to the “t” in the English word “touch”.
1. [d] [t] are alveolar plosive initials.
2. Vocal cord: [d] [t] are both voiceless.