Must, to have to

Students of class III A are studying must and to have to.

here are some useful exercises to review what we have already studied at school. 

http://www.englishexercises.org/makeagame/viewgame.asp?id=9977

http://www.englishexercises.org/makeagame/viewgame.asp?id=8969

http://www.englishexercises.org/makeagame/viewgame.asp?id=6958