change following into: a) a general question b) question with a tag 
1. We often have dictations in class
2. Studens write a lot of sentences on the blackboard
3. According to the timetable we shall attend six hours a day
4. Comprehensive schools combined all types of secondary education 

1. Do we often have dictations in class? We often have dictations in class, don't we?2. Do studens write a lot of sentences on the blackboard? Studens write a lot of sentences on the blackboar, don't they?3. Shall we attend six hours a day according to the timetable? According to the timetable we shall attend six hours a day, shan't we?4. Did comprehensive schools combine all types of secondary education? Comprehensive schools combined all types of secondary education, didn't they?

1. Do we often have dictations in class?    We often have dictations in class, don't we?2. Do studens write a lot of sentences on the blackboard?    Studens write a lot of sentences on the blackboard, don't they?3. Shall we attend six hours a day according to the timetable?    According to the timetable we shall attend six hours a day, shan't we?4. Did comprehensive schools combine all types of secondary education?    Comprehensive schools combined all types of secondary education, didn't they?