Vídeo com explicação: https://www.youtube.com/watch?v=XpA_McVjorM
Link 1: http://www.usefulenglish.ru/grammar/modal-verbs-exercise-four
Link 2: http://www.usefulenglish.ru/grammar/modal-verbs-exercise-one
Link 3: http://www.usefulenglish.ru/vocabulary/synonyms-exercise-five
