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A
Asking the customer their age
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B
Checking a valid, government-issued photo identification
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C
Judging by their appearance
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D
Asking other customers
Why this is the answer
The most reliable way to verify age is to check a valid, government-issued photo ID — such as a driver's license, state ID card, military ID, or passport — that shows the customer's date of birth and photo. Relying on appearance or simply asking the customer's age is not sufficient and is not a defense if the person turns out to be underage. Carefully examining a valid ID is the standard responsible-service practice and the seller's best protection against an illegal sale to a minor.
Source: Responsible Beverage Service — ID Verification