Answer — Exercise 9
14 - What a load of rubbish!·Outcomes Pre-Intermediate - Student's Book
Question
Look at the extracts and decide if must / mustn’t can be replaces by have to / don’t have to.
Answer
- In a and b, must can be replaced by have to because it means something is essential.
- c must can’t be replaced by have to because it means ‘I imagine this is definitely true’.
- d mustn’t can’t be replaced by don’t have to, the meanings are totally different: mustn’t means it is not permitted / not allowed, whereas don’t have to means there is no obligation, it’s not necessary (but you can do it if you want to).