A cashier notices a person, who appears to be underage, passing money to a customer who is entering the store. The underage person waits outside while the customer puts a six$-$pack of beer on the cashier's counter. What should the cashier do$?$

Sell the beer if the customer purchasing the alcohol has valid identification.

Refuse the sale because she suspects the customer is buying alcohol for an underage person.

Sell the beer if the customer denies buying it for the underage person when asked.

Call the police.