Must/mustn't/have to/don't have to
CORRECT THE MISTAKE: "The skatepark is free = we haven't to pay anything."
We DON'T HAVE TO pay anything.
CORRECT THE MISTAKE: "You must to bring your pencil case to the next lesson."
You MUST BRING your pencil case to the next lesson.
CORRECT THE MISTAKE: "We mustn't bring food to the party - Jake's mum is making everything."
We DON'T HAVE TO bring food to the party.