Answer:
The correct answer is D. Slow down and use shorter phrases.
Step-by-step explanation:
Projecting the voice means that your voice can be heard clearly, that it is easy to understand the words you are saying, that the natural sound of your voice is not altered in any way, both at low and high volume, all this maintaining a healthy vocal production, free of tensions.
You may be surprised to have read that the voice can be projected at a low volume, since there are many people who "project the voice" means "to hear more."