Which of the following beers is an example of a Fruity-Sour style?

The choice of Stupid Silly Sour as an example of a Fruity-Sour style beer is correct because this style is characterized by its tart and sometimes fruity flavors, often derived from the use of specific yeast strains or the addition of fruits during fermentation. Fruity-Sour beers typically have a lively acidity and can showcase a variety of fruit flavors, providing a refreshing and complex taste experience.

In contrast, options like Guinness Stout and Rogue Nitro Chocolate Stout are examples of darker, malt-forward beers that emphasize rich, roasted flavors rather than sourness or fruitiness. House Belgian Amber Tripel is a Belgian-style beer that may have some fruity notes due to its yeast, but it is not specifically classified as a Fruity-Sour beer; it usually leans more towards being a strong ale with a sweeter profile. Therefore, Stupid Silly Sour stands out as the clear representative of the Fruity-Sour style.