Could you please help me describe the pictures I posted you and check these sentences.

Question

1) Go and fetch some chalk, will you?
Open the window halfway to let some fresh air in.
2) You should hand in your dissertation by next Monday.
Wipe off the blackboard.
3) If you enter the classroom ten minutes after your lesson starts, you won't be let in.
4) Your parents justify your absence by filling and signing the excuse slip.