Which of the following is part of a Brass Monkey cocktail?

The Brass Monkey cocktail is traditionally known to contain dark rum, which is a key component that contributes to its distinctive flavor. Dark rum provides a rich, molasses-like sweetness, which balances well with other ingredients in the drink. This particular cocktail often combines dark rum with orange juice and possibly other ingredients, making it a refreshing choice.

While gin, whiskey, and tequila are popular spirits used in many cocktails, they are not typically included in a Brass Monkey. Each of these alternatives has its own unique flavor profile that would not align with the characteristic taste and style of a Brass Monkey cocktail. Therefore, the selection of dark rum as the correct answer underscores its essential role in defining this iconic drink.