1. mai ( not; see) the play every often
=> Mai does not see the play very often
2. he said he ( not ; know ) her address
=> He said he did not know her address
3. tomorrow when he come we ( go ) shopping 
=> Tomorrow when he come we will go shopping
4. i ( send ) you a letter when i come to london next month
=> I will send a letter..
5. (not throw) trash over there
=> Do not throw trash..
6. chirdren  must ( take ) part in activities with others
=> Chilsren must take part in...
7.( you; come ) to hanoi last month 
=> Did you come to hanoi last month
=> You came to hanoi last month
8. how much is ( cost ; mail) a letter to E
=> How much is the mail cost..
9. i prefer ( chat ) with my friend 
=> I prefer to chat
10. she ought ( study ) hard
=> She ought to study hard