Which of the following is an example of a highball cocktail?

A highball cocktail is characterized by a simple blend of a spirit and a larger proportion of a non-alcoholic mixer, typically served over ice in a tall glass. The Cuba Libre is a quintessential example of a highball cocktail, as it consists of rum, cola, and lime, served over ice in a highball glass.

In contrast, the Martini, which is primarily made with gin and vermouth, is a mixed drink served in a stemmed glass, typically without a significant non-alcoholic mixer. The Old Fashioned is a spirit-forward cocktail that includes whiskey, bitters, sugar, and often a twist of citrus, served in a short glass and not involving a highball composition. Similarly, the Negroni consists of equal parts gin, vermouth, and Campari, also served in a short glass and does not fit the highball mold.

These distinctions highlight why the Cuba Libre is the appropriate example of a highball cocktail due to its composition and serving style.