Rewrite the sentences without changing their meanings

VI. Rewrite the sentences without changing their meanings. 
37: Be good or your parents will unhappy.
      => If __________________________
38: Does your friend like this cake? (tag question)
      => Your_______________________________
39: Mary last visited Hue 3 years ago.
      => Mary has_________________
40: Liz found it hard to leave behind her friends.
      => It was___________________________