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A
Card no one
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B
Card anyone who appears under a set age (such as 30 or 40), or card everyone
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C
Card only people who look nervous
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D
Card only on weekends
Why this is the answer
A common and safe house policy is to card anyone who appears to be under a generous threshold age — such as 30 or 40 — or simply to card every customer regardless of apparent age. Because people's apparent age can be misleading, setting the carding threshold well above 21 reduces the chance of missing a minor. Carding everyone removes guesswork entirely and avoids any appearance of discrimination. Servers should follow their establishment's specific carding policy, which is often stricter than the bare legal minimum.
Source: Responsible Beverage Service — Carding Policy