why "di que hace?
Why not dice que hacen?
It depends on the subject. If the subject (third person) is in singular form (example: he, she, etc.) you use "hace", but if it's in plural form (ex: they) you use "hacen".
Check out Lesson 1.4 if you want to study furthermore.
Welcome to the forum, PhDig! In the future, try to provide as much detail and context as possible in your original post, and try not to re-post your own questions.
PhDig do you have a sentence or a paragraph that this goes with? Without context it's a bit hard to help you.