Complete the sentences using the modal verbs provided.

Here are the completed sentences: 10. You needn't go to the party if you don't want to. 11. I must tidy my room before going out. 12. I can't play badminton as I find it difficult. 13. He has to wear a helmet at work for safety reasons. 14. I couldn't swim very fast when I was eight years old. 15. You ought to be polite to older people as a sign of respect.