What is a common characteristic of a Black Russian and a White Russian?

A common characteristic of both a Black Russian and a White Russian is that they contain vodka. The Black Russian is a simple cocktail made with vodka and coffee liqueur, typically served in a lowball glass. The White Russian expands upon this by adding cream or milk to the vodka and coffee liqueur mixture, creating a richer and smoother texture. Therefore, the fact that both cocktails include vodka highlights this essential ingredient that links them together.

The other options don't hold true: while presentation can vary, they are not specifically served in tall glasses, nor do both cocktails share the characteristic of not containing cream since the White Russian does include cream. Additionally, neither of these cocktails features rum as a primary ingredient; they are primarily vodka-based drinks.