You have to wear a helmet when riding a motorcycle. - Strong obligation – It’s necessary or required (often by rules or authority)., You don’t have to bring your own pen; we’ll provide one. - No obligation – It’s optional; you’re not required to., You must not smoke in this building. - Prohibition – It is forbidden., You should eat more vegetables for better health. - Advice – A recommendation for good behavior or outcome., You must arrive at the airport three hours before your flight. - Very strong obligation – Usually due to external rules or safety., You shouldn’t stay up so late before an exam. - Negative advice – It’s not a good idea to do this.,

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