Ответ:

  1. What are your plans for the weekend? We will stay at home. — A) will stay.
  2. We usually have five classes a day. — B) have.
  3. I am going to the dentist today. — B) am going.
  4. He often plays football with his friends after school. — C) plays.

Will expresses a future plan or decision, the Present Simple is used for routines, and the Present Continuous is used for an arrangement happening today. After he, the verb takes the ending -s.