1`he were painting a world map when i left there
2`what were they doing when you saw them? they were cleaning the classroom
3`at that time, the students of class two weren't playing the football,they were playing the basketball
4`one day, the mother get off work to take part meeting,John were write a letter to one of his friend.
5`firday afternoon,what were students doing?
they keep posting the poster to the wall.
6`this time yesterday,some students are planting saplings,some students are watering these saplings.