MUST, HAVE TO, MUSTN'T, DON'T HAVE TO

http://www.ejerciciodeingles.com/ejercicios-verbos-modales-must-have-to-expresar-obligacion-rellenar-huecos/
http://www.aulafacil.com/cursos/l22659/idiomas/ingles/ingles-repaso-de-gramatica/ejercicios-must-have-to
http://mbonillo.xavierre.com/exercises/eso4/4eso2007/musthaveto1.htm

http://www.agendaweb.org/verbs/modals-must-have-to-exercises.html