What are banner ads typically characterized by?

Banner ads are primarily characterized by having standard dimensions, such as 300x250 pixels. This standardization ensures consistency in design and facilitates the ad placement process across various platforms and websites. These specific dimensions have become widely accepted within the digital advertising industry, allowing advertisers to effectively create ads that are easily recognizable and fit within the layouts of web pages.

The other options do not accurately describe banner ads. For instance, while some ads may experiment with audio elements, this is not a characteristic typically associated with standard banner ads, which are primarily visual. Similarly, banner ads are not exclusive to mobile devices; they are widely used across desktop platforms as well. Lastly, video content is not a defining feature of banner ads, which typically consist of static or animated graphics rather than video. Overall, the correct answer highlights the fundamental aspect of banner ads that makes them effective and versatile in digital advertising.