1) Make the sentences interrogative and negative:
      a) I have to take a taxi.
      b) We are able to meet at 5 o'clock.
      c) You may doit yourself.
2) Put the  sentences in the Past and Future Tense:
      a) You must tell us a story.
      b) We can't go together.
      c) She may take the book.
3) Use modal verbs or their equivalents :
      a) ... you do this work now
      b) I ... (not) to visit you next Sunday, because I ... to meet my brother.
      c) As the weather was fine, we ... to go to the country.
      d) They ... use a dictionary during their examp.