Complete the sentences with can/can't, must/mustn't or may. 
1-You  forget to offer your mother a present on Mother's day.
 
2-You  brush your teeth regularly.
 
3-Birds fly but elephants
 
4-It rain this afternoon. There are many grey clouds in the sky.
 
5- you lend me some money, please?
 
6-I  speak French but I can't write it .
 
7-You  eat or sleep in class.
 
8-Students switch off their mobile phones in class.
 
9- Surfing the net  become an addiction.
 
10- The lesson is over pupils. You leave now.Good bye.
 
11- You  borrow three books a week from our library.
 
12-Medicines  cure us when we are ill but they  be harmful if we take them without our doctor's prescription.
 
13-Teachers and students  go to school late.
 
14-I  ski at any time of the day here but I  bring my equipment first.
 
15-We  help the elderly as much as we can.