The key to exercise solutions in chapter 7 - Language focus for the textbook New Headway Upper-Intermediate - Workbook with authors Liz Soars, John Soars and Paul Hancock from Oxford University Press
Question
Rewrite the sentences to give the opposite meaning.
Answer
You mustn't / can't stop here.
We don't have to / needn't learn the whole poem.
They didn't have to take off their shoes.
He can't be speaking Swedish.
You don't have to / don't need to help me do this exercise.