Which of the following drinks can use flex shots?

Flex shots refer to a specific variety of espresso shots that are often incorporated into blended drinks, such as Chillers at Black Rock Coffee Bar. These drinks are designed to be customizable and can include various flavor options, allowing for a unique coffee experience that appeals to a broad range of tastes. The use of flex shots in Chillers enhances their flavor profile, creating a richer and more satisfying beverage.

The other drink options do not typically utilize flex shots in the same way. Espresso shots are standard and do not have the flexibility associated with those used in blended drinks. Black coffee is usually served without any added variations that flex shots would provide. Cold brew, while delicious in its own right, is brewed in a way that does not incorporate the espresso shot at all. Thus, Chillers stand out as the appropriate choice for using flex shots, highlighting their customizable nature and the blend of flavors they can provide.