modal verbs sites (sitios para alclarar el significado y uso)

http://menuaingles.blogspot.com/2007/03/had-better.html




http://elblogdelingles.blogspot.com/2006/06/lesson-23-ought-to-modal-verbs-vii.html



http://www.clafoti.com/imagenes12/should.htm



http://www.aulafacil.com/CursoIngles/Clase44.htm



http://menuaingles.blogspot.com/2007/11/formas-negativas-de-may-might-can.html