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You and your friends hear a knock at the door. Select ALL the sentences that make a correct logical deduction.
Context: You ordered a pizza 10 minutes ago, but the restaurant said delivery takes 45 minutes. Your best friend Sarah promised to arrive at exactly 8:00 PM. It is now 8:00 PM, and someone is knocking.
The correct answers are It must be Sarah. and It can't be the pizza delivery.
When we are almost 100% sure something is true based on evidence, we use must (It must be Sarah).
When we are almost 100% sure something is not true, we use can't (It can't be the pizza).
Can is not used for specific present deductions. Mustn't is usually used for prohibition (rules against doing something), not for negative deductions.