○ 正解です。

'Must' and 'have to' mean about the same thing but 'must not' and 'don't have to' are very different.
'Must not' means that something is not permitted (してはならない)(禁止)
'Can't' means something is impossible (不可能) or not permitted (禁止).
'Don't have to' means there is no need to do something (する必要がありません).