Help the secret agent understand the rather alarming warning label on his new spy car. Choose the correct phrase to complete the sentence.

"You can deploy the oil slick whenever you like, but you ______ press the big red button, or the car will instantly self-destruct!"

The correct answer is mustn't.

We use mustn't (must not) to express a strong prohibition—it means "do not do this" or "it is forbidden."

Don't have to means something is optional (you can do it if you want, but it's not required), which would be a terrible instruction for a self-destruct button!