What ingredient must be added to the middle line when making the Tall Eggnog Frappuccino?

To create a Tall Eggnog Frappuccino, it is essential to include eggnog as a key ingredient. Eggnog is the signature flavor of this seasonal drink, providing the creamy texture and characteristic taste that defines the beverage. When preparing the frappuccino, eggnog is used both as a base and flavoring agent, differentiating it from other frappuccino options. Using eggnog ensures that customers receive the festive experience they're expecting, especially since this drink is typically offered during the holiday season.

The other options do not align with the traditional recipe for an Eggnog Frappuccino; therefore, they would not fulfill the requirement of the drink being properly categorized as such.