The document provides a grammar exercise on modals such as "can-can't", "must-mustn't", "have to-don't have to". It contains 3 parts with multiple choice questions to test understanding of ability and obligation. Part A contains sentences to be filled in with "can or can't". Part B contains sentences to be filled in with "can-can't or must-mustn't". Part C contains sentences to be filled in with "must-mustn't or have to-don't have to". The answers or keys are provided at the end.