What fills the Vermouth Cassis cocktail alongside Dry Vermouth and Creme de Cassis?

In the Vermouth Cassis cocktail, the combination of Dry Vermouth and Creme de Cassis is complemented by soda. The addition of soda serves several purposes: it lightens the drink, adds a refreshing effervescence, and balances the richness of the Creme de Cassis, which is a sweet blackcurrant liqueur. Using soda helps to create a more approachable and enjoyable cocktail that's not overly sweet or heavy, making it a popular choice for those looking for a refreshing beverage.

Soda enhances the overall flavor profile and textural experience, ensuring that the cocktail is well-rounded and easy to sip. This is key in many cocktail preparations where carbonated elements are used to elevate the drink without overpowering its other flavors.

The other choices, such as orange juice, pineapple juice, and grenadine, do not align with traditional recipes for a Vermouth Cassis cocktail and would alter the intended balance and taste, leading to a very different drink.