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You are reading a top-secret manual for surviving a vampire attack. Select ALL the grammatically correct options to complete this crucial safety rule.
"If you hear a knock at your window at midnight, you ________ keep the door locked!"
The correct answers are must, have to, and have got to.
All three of these options correctly express strong obligation or necessity for the pronoun "you".
Have got to is a slightly more informal (but perfectly correct) way to say have to.
"Must to" is incorrect because modal verbs are followed by a bare infinitive (no "to"). "Has to" is incorrect because it is only used for third-person singular subjects (he/she/it).