Which of the following is a trait of an Imperial Stout?

An Imperial Stout is characterized by its assertive roast flavor, which is a key trait of this style of stout. The brewing process typically involves dark malts that provide rich, roasted notes and a strong coffee or chocolate character, which are prominent in Imperial Stouts. This bold flavor profile is enhanced by the beer's higher alcohol content, differentiating it from standard stouts, which may have milder flavors.

The other characteristics presented in the options do not align with the defining traits of an Imperial Stout. For example, light body and low alcohol content are more representative of lighter beer styles rather than a fuller, more complex beer like an Imperial Stout. Fruity aroma, while it can be found in some beer styles, is not a hallmark of Imperial Stouts, which focus more on roasted malt flavors rather than fruity characteristics. Thus, the defining feature of an assertive roast flavor is what solidifies B as the correct choice.