Which ingredient listed is a primary component of a Rob Roy?

The primary component of a Rob Roy is Scotch whiskey, making the selection of Scotch the correct answer. The Rob Roy is essentially a variation of a Manhattan, but instead of bourbon or rye whiskey, it specifically uses Scotch as its base. This choice of whisky provides the distinctive flavors and characteristics that define the cocktail.

The drink is typically mixed with sweet vermouth and bitters, resulting in a rich and flavorful experience that showcases the uniqueness of Scotch. The use of other spirits, such as rum or vodka, would fundamentally alter the nature of the cocktail, distancing it from its classic definition. Therefore, choosing Scotch as a primary ingredient is crucial for maintaining the integrity and flavor profile of the Rob Roy.