mustn't / don't have to
It is forbidden. You ______ do that.    You ______ ask my permission. You can do what you want.    You ______ speak to the driver when the bus is moving. It's dangerous.    Help yourself to anything you want. You ______ ask.    You ______ park here. There is a double yellow line.    Pay me back when you can. You ______ do it immediately.    It's optional. We ______ to go if you don't want to.    I'll tell you a secret. You ______ tell anybody else. Promise?    Whatever you do, you ______ click with the right mouse button or the program will crash.    Be on time. You ______ be late or we will leave without you.    He's a millionaire. He ______ work but he does because he enjoys it.    I like Saturdays because I ______ go to work.    This is very important. You ______ forget what I said.    It's very infomal here. You ______ wear a tie unless you want to.    The train is direct. You ______ change trains.    In boxing, you ______ hit your opponent below the belt.    I ______ wear a suit at work on Fridays. It's 'dressing down day".    In athletics, you ______ start before the gun is fired.    In bridge, you ______ look at other people's cards.    You ______ be mad to work here but it helps.