Answer:
1- Vosotros van a hacer ejercicio.
2- Vosotros hacéis ejercicio.
3- Dora va a leer una novela.
Explanation:
1- In the first case, it is a sentence that refers to the future, where the second person of the plural ("vosotros") will carry out a certain activity in the near future. Thus, the phrase "vosotros van a hacer" is equal to "you are going to do", which shows the time in which the action will take place.
2- In the second case, time passes from future to present, with which the action takes place in the moment. Therefore, people are not going to do something, but are doing it in the present tense, with which "van a hacer" becomes "hacéis."
3- In the third case the same situation occurs as in the first, where the person (in this case the third person singular) is going to perform an action in the near future.